Here is a good article from ilovebicycling
Descending on a bike can be intense! The main focuses while descending are improving your technique, confidence, awareness, anticipation and safety.
The most important factor to improve descending on a bike is to focus on your technique. Try to lower your centre of gravity by riding on the drops on a road bike, this will give you more stopping power and greater control. Also try to stay relaxed and the corners will become more fluid.
If you are looking to increase your speed while descending then get more aero by tucking your elbows in, lowering your head and keeping your knees in. Also make sure to pick the shortest line by entering the corner wide and cutting the corner as much as safely possible through the apex and exiting wide.
To decelerate as quickly as possible use do not forget to use the front brake as this is where most of the stopping power is while going downhill. Additionally, anticipate how much you need to slow down before you enter the cornerbecause when you try to brake mid corner the bike will try and stand up on you making the corner much more difficult to navigate. Not slowing down enough before a corner while descending is the most common error an amateur will make… they will come in hot, try to brake mid corner forcing them to slow down much more than necessary and exiting the corner at a slow speed. Ideally you brake before the corner, lower your centre of gravity, push your outside foot down on the outside pedal, push down on your inside handlebar (not braking mid turn) while exiting with speed.
Confidence is key. Second guessing actions leads to mistakes. Practice will inevitably beat confidence in to you; however, if you feel that is not quick enough… start descending slower in a zone that you are comfortable and relaxed. Practice your technique and skills and then continuously increase your speed as confidence rises. Watch other peoples lines and technique and adopt what works. Confidence will come with repetition and becoming comfortable with your limits.
Awareness and Anticipation
Awareness while descending on a road bike can mean watching out for cars, people, potholes and other cyclists; while, descending on mountain bike can mean watching out for rocks, logs, drops and loose dirt. Either way awareness is key while descending a hill so that you can anticipate what is coming and how to react. Keeping your eyes focused on what lies well ahead of you is paramount.
Safety never taking a holiday is never more true on a bike than when descending. Some cyclists will reach upwards of 60 miles per hour (100 kilometres per hour) while descending. Going downhill is safest when your technique is tried and true, your confidence is high but not unrealistic and you are aware and anticipating what is coming next.
Never cross the centre line of a road to take a corner faster, and go slow enough to be able to dodge unexpected obstacles! Getting injured because you are trying to push the limits too much is never worth it.