Also try gripping with different parts of your legs to stay up forward on the bike - the obvious grip is with thighs, but you can also grip with your heels, while the balls of your feet are pushing down and out against sharp pegs... For MX, you may want to lower your clutch and brake levers slightly, helping to keep your elbows up. MX "attack' position is head over the bars slightly with elbows up so you can move your upper body side to side comfortably. Watch a pro rider from the front and side to see how he is positioned on the bike standing and sitting - many times they look like they are trying to get out in front of their own bike. Like RayRay is saying - avoid being pulled by the bike, be propelled by it. And, another good place to rest is in the air! (although I don't!!)
