Usually its just a matter of practicing and building up your ankles and legs. After a while, your body because comfort with the board and just reacts naturally to the sight changes in your board when you're going DH to the point where it's just an involuntary reaction. Being nervous and thinking if you're going to crash doesn't help. Just take it slow till you build up the confidence and experience.
I say usually the rider, but it can also be the gear too. I used to get them all the time, but to help I would tighten the trucks, and ride, and after a while start to loosen them bit by bit as I got comfortable.