down hill tips.

First learn to trust your brakes.
-one or two fingers only
-front brake is most powerful.

Try this. Find a steep, straight section of trail. Go down it using only your rear brake. Then, just your front. Then, both.
What you will find it that you can't descend with only your rear brake: it grabs and skids and pull you sideways. You will find that you CAN descend using just your front if you modulate: use gentle pressure. Using both brakes your goal is to go as slow as possible without skidding. The microsecond you start to feel your (rear) wheel lock up, just let off the brake a bit.

Now that you have more faith in your brakes, don't use them so much. Remember to look where you want to go, your body position, and that momentum is your friend. Also, if your butt is too far back you lose control of the front of the bike.

If you have the opportunity to do lift served biking DO IT. It's not just for downhillers. It's a great way to get comfortable with speed on easy trails.