When learning to jump firstly make sure you're padded up.
Secondly, best to bounce with a pole infront of you for stability. This allows u to concentrate your efforts in the bounce rather than balance.
Once you've worked out "the physics" of jumping, release the pole.
Try not to lean forward too much (else you'll bail on landing), upright as much as possible.
To gain height, SLAM from your heels down as you land.
WARNING: Dont slam too hard else you'll bottom out, you'll know about it if you do!