1.this is the exact same thing as a b/s 180 except you're turning the other way.
2.put your back foot on the heel edge corner of the tail and your front foot a little closer to the toe edge than an ollie.
3.turn your upper body slightly so your back is towards the nose. right before you ollie, start untwisting and then turn your body 180 after you ollie. (it should be one fluent motion)