Find a nice long hill without ideal traction and try riding up and while you go up, shift you weight forward and backward. To far forward the you wheel spins, shift and bit back and you will find the traction, too far back and the front end lifts. Its amazing to see what a subtle movement on the bike does. Try again with legs fully extended then bent and you see the effect of crouching down on the bike.
Going down, get your butt down on the fender as far back as you can - again keep you CG as low as possible.
K