Set your feet up as you would for a normal nollie, but keep your shoulders and back slightly more parallel with the board than usual.
Step2
Pop your front foot down as hard as possible to get the maximum pop, and begin to turn your shoulders and hips backside as you go up.
Step3
Suck your legs up, and use your upper body to guide the turn. Don't turn completely 180 on your way up (as you would for a frontside 180 nollie); you will inevitably over-rotate in the air and land at a crooked angle, sending you flying backwards to your head.
Step4
Turn only 90 degrees on your way to the peak height of the trick (so you are only half way through your turn).
Step5
Clear the obstacle or go as high as you are going to go.
Step6
Relax your body and let the natural leftover momentum carry you the rest of the 180-degree turn.
Step7
Land as solidly as possible (all four wheels), let your knees absorb the impact, turn around, and do another one!