Two ways to do this:
The real way:
-Level the pedals
-Compress your body down and also the tires by pushing down and bending 
 your knees and arms.
-When you want to take off, pull the handlebar to your chest and move 
 your weight back.  This will give you a small wheelie.
-When you are going up, push the bar up and forward, twisting the grip 
 at the same time.  While you are doing this, unweight the back end of the 
 bike by leaning forward and really extend your arms.  The saddle might
 hit your chest, but that's ok.
-Relax your body before hitting the ground.
-Land with some weight in the back so that the back wheel hits the ground 
 first.  Make sure your front wheel is straight before you land.

The SPD/toe-clip way:
-Again, preload your body by coiling down and pressing real hard down.
-Instead of doing all the weight shifting, just jump and yank up real hard.  
-Landing is the same.