Basic rules of descending:
The hard braking MUST be done before the corner. I cannot emphasize that enough. It's faster on a descent, and safer, to brake a bit too hard on the way into a corner and take a good line though the corner, than it is to hope you can make it around the corner because you went into the turn too fast. If you're on the brakes fairly hard half way around a bend then you went in too fast.
Always look way, way up the road - not just at the point where you're going to be. This requires practice over time. The more you do it the more you gain confidence. Vision is everything. Example: You're coming down a hill and approaching what looks like a hairpin bend that turns to the left. You apply the brakes, look at the bend and then look down the hill across you left shoulder to see where the road goes after the bend. That look only needs to take a second but provides a lot of information. It may be that what looks to be a hairpin bend really isn't - it might be that what looks like an easy corner is really a very, very tight corner. Vision is everything. Just like with a car, don't go faster than you can stay safe.
Bikes don't turn well when they're pretty much upright. You need me make the bike lean. The easiest way to make a bike lean into a corner when you start to turn, it to turn the bars ever so slightly the opposite way for a brief moment. This is a bit of an 'advanced' technique and it's one that motorcycle guys embrace as "rear wheel steering" - the difference is they can stay on the power during the corner, keep that opposite turn and steer with the throttle, whereas on a bicycle you can only do it for a fraction of a second or you'll fall on your ass.
All it takes it to move your body a little to the outside of the turn (if you're turning left, then put your weight a little bit more on the right side of the bike) and less than a centimeter of movement in the handlebars in the opposite direction of the turn, smoothly but quickly, to get the bike to want to lean into the corner. Once the bike starts to "drop", turn the wheel in the direction of the inside of the corner. As with everything on the bike, start slow and gain confidence before progressing.
The best way of going fast downhill: Follow someone fast. Bike clubs are a good place for this. Ride with others that are better than you.