so nice job explaining it guys and ill just throw something else in, its all about your stance, balance and edges.
Have a good relaxed stance, knees bent, back straight, shoulders pointed where your going and eyes up!
be relaxed but maintain good balance.
you want to stay on your edges instead of just flat
well good luck man, one more thing: if you can avoid the flat areas, do so. you should try to become a better rider before you ride flats comfortably.
oh yeah and what tboooe said, listen to snowolf, he is probably the most experienced instructor here