I used to worry a lot more, but then I heard something that actually helped me to not worry so much.
The thing that I heard is this: things that you worry about are usually not as bad as you think. That is, if you've got a situation that's bad and you're feeling uneasy about how things will turn out, it usually happens that you make things worse in your mind than they will turn out. If there are things that are beyond your control and there's nothing that you can do about it, stop worrying about it. Forget about it. It'll turn out OK most likely- you will live, and you'll get over it or through it!