Getting Started
Before you Buy -
1.  It is recommended that you start by reading bicycle reviews,articles and talk with friends to see what they like and dislike about their bikes.
2. Take all bikes for a test drive: Make sure that the saddle is adjusted properly. Also make sure that you aren't stretching to reach the handlebars or are too cramped.
3. Ensure that the wheels are secure in the forks and that the quick-release levers are tight. Also check to see that the headset is tight, if its not the bike will not be considered under warranty. While checking the headset, make sure that the handlebars are correctly positioned in the frame, Push down hard on the handlebars as well to see if anything is loose, e.g. brake levers or shifters.
4. Don't allow a pushy salesperson to coax you into buying a bike that you don't really know anything about. You should be in FULL control of the purchase, not the salesperson. This is why it may be a good idea to research exactly what you are looking for before you start looking.
5. Check to see that you are buying the right size. Many times, the salesperson will want to set you up on a bike that is on the floor even though it may not be the right size. When you stand over a bike, there should be between 3 and 5 inches between the top of the frame and your crotch.
6. Look around at other bike shops or in catalogs to see if you are paying more for your bike than you should be.
7. If the bike is being sold at a very low price, don't hesitate to ask the retailer why the bike is going for that price. There could be a defect which would cause for a loss of warranty.
8. If you are offered any kind of free tune up after purchasing your bike, make sure the offer is in writing and that you remember to bring it in. This will allow for any adjustments to be made if the bike had not been set up properly. After a month or so of use, the cables on the bike tend to slack out - this is the best time to take your bike in because you don't have to pay for them to get tightened. If you do not have your cables tightened to the correct amount, your shifting or braking may be effected.
9. If you feel that you don't really know too much about bikes, bring a friend along who knows more about them and can ask helpful questions.

 Things to Consider-
1. Try to set a budget for yourself so that you will only look at bikes that are in your price range. This will make it easier on you to choose one you like and feel comfortable forking the cash over for.
2. Try to assess how much riding you'll be doing and on what kinds of terrain.
3. Do as much research on your possible purchase as you can. Collect booklets on each bike and then compare them to see which bike has the components you want.
4. Try to test ride each bike that you've been looking at because there's no better comparison then actually riding.
5. If you are intending to buy a second-hand bike, ask a local bike shop to look it over for you to make sure everything is working properly. Also, ask the seller for the original sales receipt to prove that the bike wasn't stolen. You should also find out what types of riding the seller used the bike for to make sure that the bike isn't worn out.

The Bike

Cogset - This is a very important part of your bike. This, along with the three rings attached to your cranks comprise the gears Gearing usually includes 21 speed and 24 speed.
Rear Derailleur - This gizmo moves the chain up and down the cogset according to how you shift the gears on the handlebar.
Brakes - Mid-range mountain bikes come equipped with cantilever brakes. These are very powerful and are even better when M-system pads are added (such at the Shimano V-Brake).
Tires - Make sure that the tires are suitable for off-road use. If they are not knobby and don't have a lot of traction, you should look into a new set.
Chain - This is what allows your bike to move. It is comprised of a hundred or so links that are connected by small pins.
Pedals - There are many different types of pedals; bear claw, bear claw with toe-clips attached and clipless pedals. Clipless pedals can be costly but they greatly improve your riding.
Crankset - All mountain bikes should come with a triple crankset which will allow you to ride efficiently on flats and fairly easily up hills. These are made from materials such as titanium, aluminum and most often, cro-moly.
Chainrings - There are usually three of these ranging in size. The small one allows you to climb steep hills, the big one allows you to go faster and the middle one is for normal riding.
Hubset - There is one of these in the middle of your front wheel as well as the back. They allow the wheel to attach to the bike and allow the wheel to spin.
Front Derailleur - This allows you to shift the chain from one ring to the next.
Forks - These hole your front wheel on, the front brakes are attached to them and they allow you to steer.
Brake Levers - These allow you to manipulate the brakes.
Handle Bar - This is the "control center" of your bike.
Stem - This attaches your handlebar to your forks via a long metal tube called a "steerer tube".
Saddle - You sit on this.
Seatpost - This connects your saddle to the frame of your bike.

Customizing your new bike or Extras

The best thing about buying a mid-range bike is the fact that you have money to spend on upgrading your bike. You can always find the latest accessories that are easy to install yourself at your local bike shop. The following accessories are relatively inexpensive, are easy to install and will improve your ride.

Bar Ends
If you decided to purchase bar ends, they will increase your power and control as you climb up steep hills as well as give you plenty of hand positions for riding on roads.
Toe Clips
These are great because the straps keep the ball of your foot centered over the pedal where you will get the most out of each stride. They are also very helpful for things like bunny hops because you are able to pull up on the pedals with your feet. They may take a bit of getting use to, so practice before you hit the trails!
Tires
If you are going to upgrade one thing on your bike, this is probably the best place to start. Mid-range bikes come with tires that are knobby enough to get by with on trails, but the knobbier the tire the more traction you'll have.
Saddles
Most entry-level bikes come with generic saddles. If you purchase a new saddle you can get it customized to serve your riding needs. Most mountain bikers prefer a narrower saddle because it allows you to slide back easily for going down hill or trying to get better traction.
Clipless Pedals
This is probably one of the most expensive upgrades you'll find because you have to buy the clipless pedals along witht eh shoes to fit. If you decided to install a pair of clipless pedals, you won't be sorry! You have total connection witht the pedals which means that all of your energy is focused on propelling the bike forward and isn't lost between your foot and the pedal. They are hard to get used to at first, but we're sure that you won't give them up once you've figured the out!

Adjusting your bike to the proper fit

Finding a bike that looks like what you want is easy, but fitting it is a completely different story. When you find a bike that fits properly, you will feel comfortable, relaxed and ready to hit the trails. Follow the simple adjusting steps below to make sure that you are getting the most out of your bike!

Finding the right fit - When you find a bike that fits you properly, you should have about three to four inches clearance between you and the top tube. When the seat and handlebars are adjusted at the same height, you should be able to sit comfortably on the bike. You will have more control over the bike if you are relaxed because it is easier to balance and if you are stretching too far it's more difficult to balance.
Adjusting the saddle height - When you first begin riding, keep the saddle on the low-end and then raise it as you become more experienced. Your feet should touch the pedals when your knee is straight and the pedal is at the lowest point.
Adjusting the saddle position - As a rule, you should have about 2 inches adjustment on the rails of your saddle. There is no set standard to decide when it is adjusted properly because it's personal preference. Try adjusting the position until you find one that works well for you.
Adjusting the handlebars - Most stems have about 1 to 2 inches of extra stem to adjust the height. Most people find that if the handlebars are adjusted below the saddle then the handlebars are more comfortable to hold on to. If you want to take the scientific approach, look at it this way: if your arms are extended at a 45 degree angle with your arms slightly bent then your handlebars are adjusted properly.

Riding Skills

Basic riding position
Elbows relaxed, bend at about 90 degrees.
Grip the bar firmly, but not too hard. If you see white knuckles, then you are gripping too tight.
Keep your back straight, at about 45 degrees from the ground surface.
Try to "stand" on the pedals. You still sit on the seat, but you don't place all your weight on it.
When not pedalling, always keep your pedals level.
You may want to add that your grips should be about shoulder length apart, but that would only really affect small/large people.
You could mention that you can (or may have to) ride with pedals vertical (&/or with one foot loose) in tight turns.

Turning
Brake before going into the turn, using both brakes.
If you have a lot of traction:
Push the outside foot down and lean to the inside (if you have traction).
Enter the corner wide, hit the apex with the bike near the inside edge and leave the corner wide.
Do not use the front brake if you are turning at the bike's limit. The front tire is using all its traction for turning. If you use your front brake, it will lose its grip and wash out. A front wheel slide is almost impossible to recover. A back end slide is easier to recover. Also, the brake tire is doing less work than the front, therefore, you can use some of its "spare" traction for braking.

If you are turning on loose surfaces, keep this in mind:
This technique involves keeping the bike relatively upright; instead, the body is leaned in the direction of the turn.
Transfer weight slightly forward. Push down on the outside pedal.
Twist your upper body to face the trail. Align your upper body so that your upper body is slightly leaning toward the inside of the turn.
Push down on handlebar on the outside and pull up on the inside.
In loose stuff, steering is definitely the preferred way to turn. This is the reason many roadies with good bike skills cannot handle tight singletrack very well.
To steer, put your weight on the inside of the turn. Turn your front wheel toward the turn, and hold your bike upright. Even if one or both of your wheels begin to skid you can easily recover. In contrast, if you lean hard through a turn on loose material and either wheel loses traction, you will be picking gravel out of your leg.
You almost always want your weight centered between your wheels. This means you move your butt further back as the terrain gets steeper. Learn to feather your front brake. Let off on the brake when your wheel hits an obstacle, and hit it harder when you have a smooth even braking surface. Many people do not learn to feather the brake, so they put their weight too far towards the rear to keep from endoing. This rear weight shift results in too little weight being placed on the front wheel, so that you cannot easily steer.
Look at the inside of the turn, not the outside. Your body tends to subconsciously point in the same direction as your eyes, so this keeps you focused on staying tight in the curve, not straying to the outer edge.
Point the inside leg in the direction of the turn (knee away from the frame), putting all weight on the outside pedal.
Push down on the inside handlebar. At this point almost all weight should be distributed between the inside grip and the outside pedal. This is much easier with a rigid fork
with a suspension fork, you really have to bear down on the handlebar.
At this point the bike is leaning under the rider, with the seat anywhere from under the thigh to just under the knee. The rider's weight is centered over the point where the two wheels are in contact with the ground, so there isn't a washout problem even in loose conditions.

This method will feel very uncomfortable at first. Pushing the handlebars away from oneself is...well, disquieting. The best way to practice this is to do figure-8 turns in a driveway. When you've got it down, hose down the driveway and then try it. If you can make sharp turns on wet concrete you can do it in loose soil.

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Braking
Most of the braking power is in the front brake because when you apply the brake, your weight shifts forward and that gives the front wheel more traction.
To maximize braking power, shift your weight back when braking.
In loose terrain, use more back brake than the front. The front has less traction because it is being "plowed".
In very steep downhill, move your weight way back, almost sitting right on the back tire.
A skidding tire will give you no control. Therefore, skidding is a very bad practice.
There are situation where you don't want to brake
Never brake when flying. If you are flying in the air (off a jump, drop off, ruts), do not touch the front brake. If you land with your front tire stopped, you can expect a huge endo.
Don't use the front brake in curves (read turning).
When going down hill, don't keep the brakes on. Instead, feather the brakes.
You might also add that the momentum of the spinning wheel can cause the bike to pitch if the wheel is stopped by the brakes.

Shifting
You must pedal in order to change gears. When changing gear, pedal lightly. It will save your drivetrain from wear and tear.
If you have "numbers" on your shifter, don't use them.
Shift before you have to. For example, when you're climbing, shift into a very low gear as you approach and start the climb. If you wait until you are about to stall it may be too late to shift.
Do not cross your gears, it will kill it. This means that you do not run a big chain ring with the large cog or the small chain ring with the small cog.
Shift lightly on the levers. There is no reason why you need to press the shifters real hard to shift.
To save the drive train from wear and tear, make sure it is clean and well lubed.

Uphills
Shift before you hit the climb. The only way to know which gear is best for your terrain is from practice. It is very hard on your drivetrain if you shift in the middle of your climb.
Seated is better for long distance and/or loose conditions. Standing is good for hammering up a short steep section with good traction.
If you find you are in too easy a gear, upshift once in the back. Do not dump a bunch of gear at once.

Seated
If you are going to stay seated, move slightly forward on the saddle.
Move your head close to the stem to keep the front from coming up.
Don't pull up on the handlebar, instead, pull backward with every stroke.
Keep your body relaxed, and shoulders square to the trail.
Put the bike in a low gear and spin.

Standing
If you decide to stand up, put the bike in a higher gear. You can't spin as fast, but you can apply more power per stroke.
Crouch down so that your butt is right in front of the saddle. Your elbows should be bent and the chest should be just above the stem.
For both methods, try to look for the smoothest line and look for slight dips on the climb. These will offer you a great opportunity to rest for a bit.

Downhills
Keep your pedals level (3 and 9 o'clock)
Get your weight back. The steeper it is, the more you move your weight. It is not uncommon to see someone riding down a hill almost sitting on their back tire.
Think positive. I had the problem of thinking I'm always out of control, but in reality, I'm not even riding close to my limits.
Shift to the middle/large chain rings. This will increase tension on the chain and you won't have so much chain slap.
Brake with mostly your rear brake. You will still need to use your front, but the back is used more often and harder.
Braking the wheel until it almost stops spinning is good. Skidding is bad.
Steer with your shoulders perpendicular to the path you want to move.
Sometimes if you can't ride down some section because it's too bumpy, you might want to add some speed.
Always be looking for your line. Identify those spots in the descent where it flattens out a little, allowing you to brake harder and "get it back". This gives you the ability to "let it go" in the more difficult parts for control because your line will take you to the part where you can "get it back."
On long descents, consider temporarily lowering the saddle, making it easier to get your butt low (or behind the seat) on steep sections.

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Front wheel wheelie
Practice on level ground with no obstacles.
Sit down and have weight slightly forward.
Shift to a low gear.
Push down hard on the pedal and shift your body weight back and pull hard on the handlebar.
Spread your knees out and try to keep your weight back. Keep pedaling.
If you feel you are going to far back, touch the back brake and you will fall back down.

Small Logs
Pop a front wheelie and land so that your front tire clears the log.
Quickly level the pedals and shift your weight forward.
Your back wheel should roll right over the log.

Logs about 1' to 2'
Pop a front wheelie and land the large chain ring on the log.
You should land with the power foot forward, about 70 degrees.
Shift your weight forward and pedal. Not too far, or you might crash.

Bunny hopping

There are two ways to do this:

The no spd/toe clip way:
Level the pedals
Compress your body down and also the tires by pushing down and bending your knees and arms.
When you want to take off, pull the handlebar to your chest and move your weight back. This will give you a small wheelie.
When you are going up, push the bar up and forward, twisting the grip at the same time. While you are doing this, unweight the back end of the bike by leaning forward and really extend your arms. The saddle might hit your chest, but that's ok.
Relax your body before hitting the ground.
Land with some weight in the back so that the back wheel hits the ground first. Make sure your front wheel is straight before you land.

The SPD/toe-clip way:
Again, preload your body by coiling down and pressing real hard down.
Instead of doing all the weight shifting, just jump and yank up real hard.
Landing is the same.

Water riding
Never ride into something that you can't see the bottom of.
If there are not too many obstacles, you can ride through the water as usual.
Instead of cranking in a high gear, try spinning in a low gear if the water is too deep.
If the water is real deep, try ratcheting your pedals by doing quarter pedal strokes.
Brakes will be much less effective when wet, so watch out.
Water can get into bearings and damage them. So don't ride things that are too deep (anything higher than your bottom bracket is considered deep by most people).
After riding through the water, pulse both brakes a few times to scrub off the water.

Mud riding
If it's just a puddle, ride in the center of it to minimize the amount of trail damage.
If it's deep and wet, spin in a low gear and keep seated so that your back end doesn't spin out.
Try to put less weight in the front. The front tire might plow into the mud, causing you to endo.
Pulse both brakes after going through the mud to scrub off the mud.
Mud, much like water, can do a lot of damage to your bike, so be careful. Also, it tends to wear out the brake pads very quickly.

Sand/Loose Stuff
Look out for the sand taking the front wheel away from your line. Weight slightly forward to keep the steering line straight. Look out for hitting this stuff too fast and burying the front wheel - instant faceplant. Really sandy trails can tire you really fast - they are easier in damp than dry conditions. Riding in sand is much like riding in mud or snow.
Keep the front end light and grind away with low gearing. If the front end is to heavy, the front tire will sink and you will endo. Good places for riding in sand are on lake beaches, river shores, or sand volleyball pits. In Wyoming, we don't have too much sand either, but do have enough so I know how to ride it.
Sand is a very difficult substance to ride on. Once you get started it is best not to stop. Turning on sand is no easy trick. Take the turn VERY gradually and do NOT lean. Leaning will simply make you fall over. Turning sharp doesn't work either, your front tire will simply plow the sand until you stop (or fall).
Sand has the same effect as sandpaper on bikes. It grinds and wears parts very quickly. Do not ride a bike you like on the beach.
The bigger the tire the better the ride when it comes to sand.
Have a positive attitude (helps in all technical scenarios).
Carry as much momentum (speed) into the pit as possible. Try to maintain this momentum as best you can.
Shift down a gear or 2 to prevent bog down. It generally doesn't help to stand.
Get the weight on the back wheel and let the front tire float a bit.
DO NOT attempt to hold a straight line by steering. The front wheel will only dig in and bury you. Allow the front wheel to drift around a bit. Keep a light touch on the steering. If you are starting to worry about your line, you can try a combo of light steering and weight shifting (one side or the other) to correct. Sometimes you will start to drift way off line and will need to steer to stay on the path. Try to start early and maintain a smooth arc. A quick move will likely fail.
Use a smooth spin. Power stroking will only break the rear wheel and slow your momentum.
If you ride in a sand infested area, consider going to wax for your lube. The sand will stick to the oil and grind away at your drivetrain.

Skidding

Braking
Skidding reduces your stopping power and increases your stopping distance. Also, you have no control over the wheel that is sliding.
All skids tend to destroy trails. If you skid a lot on your local trail and it's closed after a winter, you might be the cause.

Singletracks
Instead of staring at the edge of the trail, look forward and ahead. You will ride straighter that way.
You will notice that the middle of the trail is usually rutted. This may cause problems during turns if you go on the inside. Instead, try taking the outside line the whole turn.
Some single tracks are too narrow and too hard to ride. If that's the case, don't risk a fall. Walk it.
If you ride a lot of single track, you might want to reduce the width of the bar to reduce the chance of your hands hitting branches. Also, L-shaped barends help a lot.
Always wear eye protection. You will need it.

Switchbacks
Slow down as you enter the turn. Start outside, hit the apex of the turn on the inside and leave on the outside.
If it's real tight, stick your foot out to pivot your bike.
If you are real good, stop and bunny hop the bike straight and ride out.

Downhill:
Slow down for the corner. It's a lot faster to make the corner without dabbing no matter how slow you have to go to do it.
Stay on the uphill side of the trail as you approach the switchback. This will allow you to make the widest arc as you turn and prevent you from hitting anything at the apex of the switchback.
As you approach slowly, put your weight back and put your outside pedal down.
As you enter the corner, look at the exit where you want to go. DO NOT look at the 100' drop-off that you will fall down if you don't make the corner!
With your weight on your outside pedal and slightly back, the next step is to commit to the corner. Lean hard into the corner until you are almost falling to the inside. When this happens, ease off the brakes and let the your bike roll under yourself. This is actually really easy to do once you get started.
If you have a hard time with this last step, you can quickly modulate the brakes to adjust your balance. It works really well.
When you have passed the apex of the corner, you can let off the brakes, start accelerating, and prepare for the next switchback.
You should never skid around a switchback. You have less control and rip up the trails.

Uphill:
For uphill switchbacks, you take the same line as for DH switchbacks.
Approach the switchback with your bike on the extreme DH side of the trail so you can make the widest arc possible. Keep your weight centered.
Lean hard into the corner and pedal your bike under yourself so you don't fall to the inside. The trick is to commit to the lean.
By the time your bike is under you, you are around the switchback. Cool.
That maneuver is called a tail whip in the bmx & freestyle world, and it's a lot easier to do on a bmx bike than an MTB. 90 degrees is about all I can do too. I tried to do 180 and tacoed my rear wheel. Very easy to taco a 26 inch wheel if you don't do it right. It's not worth it try to tail whip around a switchback, just slow down, lean the bike into the turn and stick out your foot if you have to. Even better, if there is a berm on the outside of the turn, use that.
In freestyle a "tail-whip" is done by stopping the front wheel and rotating the frame around the headset, while keeping your body above the front wheel/ handlebar area. The maneuver described above doesn't have a flashy name that I know of (I just use "front wheel 180") but it IS much easier on the BMX/freestyle bike.

Hints:
Keep a little speed, just above walking pace
Start with pedals level, outside foot forward (if back end is swinging to the left, put left pedal forward)
Start turning into the spin, grab BOTH brakes (keeps the pedals from moving on you), unweight the rear wheel, and turn
Push forward on the outside bar and pull down and back on the inside use your rear/inside foot to help pull the back end around.
As you set the back end down, let go of the rear brake (or both if you want to roll backwards)
Depends on how open the sides of the trails are. Very easy to hit thick brush alongside the trail, but if it's open enough it'd work. Probably best done on the uphill loop only. I'd probably go for the trials-style hop and twist if I couldn't ride the corner. Just stop mid-turn, start hopping for balance, and then rotate until you're headed the right direction and ride away again.

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Going Down:

(Without a nose wheelie) Weight as far rearward as possible. Getting off the back of the saddle and with the butt down low is sometimes necessary. Swing up on the upper part of the switchback to enlarge the turning radius as much as possible. Use both brakes, you will need a lot of front brake to prevent a rear skid so keeping the weight rearward and on the pedals will help prevent a wheelie. You should concentrate on crouching on those pedals thus keeping as little weight as possible on the bars. Turn the wheel as steeply as you need to in order to keep the bike on the trail. At this point it becomes a balancing act. Too much weight on the outside and you go crashing down the hill, too much on the inside and you fall in that direction but at least not very far. If you must err, err to the inside. If you keep the front tire on line, the back will follow. You will find that you can turn much more sharply than you at first believe, just maintain that balance and force the turn, the bike will do the rest.

Wheelie Method:
This must first be mastered on level ground, then gradually increasing slopes on grassy hills. The idea is to grab the front brake and push forward on the bars raising the back wheel off of the ground. You then twist your lower body, basically rotating the rear of the bike along the axis of the headset as the front tire remains pointed in the original direction. As the back wheel is about to land, quickly align the front wheel with the rear of the bike and pedal away. Obviously this is a skill which takes some practice to master (on the open grass prior to trying on the switchback). First try to master balancing on the nose wheelie prior to trying to turn.

Going Up:
Usually more of a challenge. Again, swing a little toward the downhill side to give yourself as much radius as possible. You usually need to be in the lowest gear. As you start up, you will lean slightly toward the inside and keep steering on track. You should lean hard enough that if you were to stop pedalling, you would slowly fall over on the inside (which is what you will do if you slip or screw up!). The interesting part is that the driving force of your pedalling will actually hold you up. If the turn is very tight and the climb is very steep you will need a nice low granny and really need to crank it hard. To prevent yourself from doing a wheelie you may need to edge your weight forard. If you try to stand it will sometimes screw up your balance but if you are having trouble using the seated method it's worth trying. Also if you are a technical wizard you can try to wheelie halfway up and whip your tire over to the right line to finish the turn. I have usually found that this is only needed in the extremely sharp turned switchbacks on narrow trails.

One more final bit of advice, you must, in your mind, visualize yourself making the move before you actually try the move. I have found that this proper frame of mind helps more than anything else with pulling off technical moves.

If you have any tips or questions Rock And Paddle has seasoned riders and pros to review your inf. and give advice,