Don't coast going down hill, keep pedaling in a smaller gear. I find it helps me feel like I have control over the bike if I keep pedaling, and I don't get all sketchy on a hill. When you get comfortable with that, you can try not pedaling and moving yourself into more aero positions, etc.

Just think about the physics of it. The bike has a tremendous amount of energy pushing it forward; it wants to go forward rather than side to side. Keeping that in mind helps me out quite a bit.