The golden rule for descending is to relax. Your bike is not going to handle terribly well if you are hanging onto it with a kung foo death grip and all your muscles tensed up. Also remember that your bike will probably handle cornering better than you think it can.
Also given the speed you are going, it is a good idea to learn about the vanishing point. This is the point where the kerb on both sides of the road appear to intersect. If it moves towards you, you slow down; if it moves away from you, then you can allow yourself to speed up. When going through a corner look at your exit point and everything should just follow through. Also make sure you have scrubbed off your speed before going into the turn, if you believe you have gone into the corner too hot, then use a gentle application of the back brake only and lean harder.
Finally, if at the end of the decent there is a climb, then ease off, going all out downhill will use up your energy reserves you need for the climb and you will just end up blowing up halfway up the hill. On my commute I have a nice decent, however at the other end of the decent I have a nasty climb. If I go flat out down the hill, I have little in the tank left for the climb, If I just free wheel down it I can just power up the other side.