Obviously this is a pretty important area. It's a major safety skill that takes a little practice to learn. A few tips:
- Down hills. The temptation going down hills, to limit your speed and make sure you do not get out of control, is to brake the whole way down. It's recommended that you do not do this, though - the brake pad could burn out. You want to do it in spurts.
- Front brake. Many beginners use both brakes simultaneously to brake. But more experienced cyclists (and I'm not one yet) use the front brake most of the time. If you practice using the front brake, you will lose the fear of flipping over the front wheel.
- Rear brake. This is good For certain situations, especially if it's slippery or your front tire blows out.