THESE ARE FUN!!!!! Anyways here goes the tech:
1. Approach wall with the intention of doing one. Make sure that you are leaning forward and that you jump at a 45 degree angle.
2. Plant your foot up high, and immediately push off and swing your other leg upwards (Other leg is most of your momentum)
3. Your arms should have been overhead before you planted your foot, swing them AROUND. Not down, not up, but around in the direction you are going (think of radial acceleration...)
4. tuck reall hard and hope that you pushed off hard enough not to hit the wall.
5. spot landing, unfold, land, try not to hit the wall again

It just takes practice on a gym wall, the technique will click eventually. I do NOT recommend this outside, its a LOT harder. Its possible and been done but some people have messed up pretty bad....