One thing you can do, and I fell into this habit when I switched from road to mtn, is lower your saddle. Without even thinking, I'm sure you have it pretty high in order to get the correct amount of leg extension. This is great when your pounding on some easy single track or a fire road but when you get on technical downhills or just plan technical riding, you need to have the saddle down and out of the way a little bit so you can move your body weight around.