i totally agree, but there is one standard body position that is used most of the time, the attack position. put your bike on a bike stand, and stand on the pegs. Grip the bars, and bend your knees slightly. Look down and grip the bike with your knees at the seat/tank junction (where the two meet). Okay, look up again and put your head over the cross bar (if you look down, you should be able to see your number on the plate). Keep your elbows up, and there you have your standard attack position that all other positions originate from. Before you move, extend your fingers straight out onto the levers, and draw an imaginary line from your elbow to your fingers. it should be one straight line, and if your fingers are too high or low, adjust your levers until they are straight.
Go out and watch videos, and you'll see examples of this. Travis Pastrana is great and displaying this, exspecially when doing his freestyle jumps, as this is the position to use while jumping, most of the time.
While you are still fresh and willing to learn, go out to a school and learn everything you can, just like Sir High Lord said. It amazes me how people can spend a fourtune on bikes and equipment, yet they don't know how to use them correctly. If you practice without the correct technique, you are wasting your time, and may develop bad habbits that will be difficuld to rectify in the future.