Mountain biking for beginners takes a little planning and some practice. Most of the skills you want are similar to what is required for a street bike, which means: If you can ride a bike, you can learn to be a mountain biker. Practice a few of these techniques around the neighborhood before you head up a mountain.
Brakes. This is probably the most important skill to master in your mountain biking for beginners quest. Since you are facing downhill, the weight is on the front wheel. This means that your front brakes will give you the most control over your descent. Squeeze gently, but firmly to slow your progress. You may be tempted to apply a hard squeeze to the front brake if you are heading downhill uncomfortably fast, but don’t. If you stop the front wheel suddenly, neither you, nor the back wheel will stop and you’ll execute a flip worthy of an acrobat. Practice using a balance of front and back brakes on increasingly steep hills until you automatically control your speed with a combination of brakes.
Sitting. Unlike a road bike, you want to sit down on your mountain bike while going uphill. The goal is to keep your weight on the back tire to maintain traction. If the front end feels unsteady, lean forward, but keep your rear end on the seat.
Standing. Stand on the downhill portion of the ride. You want to use your legs and knees as shock absorbers to keep your trunk steady. You’ll be using your body to control the descent, so standing feels correct anyway.
Shifting. You want to be in a low gear to go uphill, but you already know this. The new thing to remember is to shift your chain onto the big ring before heading downhill. The larger ring keeps a better grip on your chain and prevents the chain from jiggling off. Having the chain on the big ring also means that if you fall, you’ll have an image of the chain pressed into your leg instead of a series of punctures from the teeth of the ring.
Pedals. While going uphill, don’t stop pedaling. It isn’t intuitive, but keeping your speed up is actually less work than pedaling slowly uphill. When heading downhill, try to keep the pedals about level with the front pedal slightly higher than the rear. It feels natural so it shouldn’t be difficult to remember to do this.
Focus and relax. You can do both. Don’t clench the bars (or your teeth) and keep your joints flexible. You use your entire body to control the bike and stiffening up any portion of it makes the bike feel rigid. Relaxing doesn’t mean not paying attention. Watch the path in front of you to prepare for rocks, bumps, divots and other hazards. Look ahead so you’re aware of drooping branches or hanging moss.
Those are the basic skills for mountain biking for beginners. Practice these on city streets before trying out your technique on an easy biking trail. Don’t choose “Mount Bike Basher” as your first run and you should be ok.