The most common error that I see from riders is not staying in a neutral riding position. If you are too far forward or too far back, then you get bucked around. Observe a SX racer in the whoops, even when hanging off the back they are able to let teh bicke rock around underneath them. Many rider simple set too far back when attempting such obstacles and pile drive the rear end or seat into their backside. Fist you need to learn to wheelie while standing over the pegs, practice lofting the wheel while standing. Once you have got that, practice smaller obstacles making note of where you body position is. If you note the bike feeling like it is coming to a stop when the rear wheel hits the obstacle, you are likely too far back and are putting LOTS of force on the rear wheel, this is bad. Personally, I like to skim or partially hit the object with my front wheel, this also lessens the chance of a slap down landing.
