What the guy above me said... yeah, first make sure you can do regular backflips. You really don't need much air at all, you can huck these on a pretty small jump before taking it bigger. Hit the jump a few times fakie to get used to it, then just rocket straight in switch, and when you hit the lip just pop hard and throw straight back. The important part is popping and then looking straight back over the top with your eyes- your body will follow your head. If you got the rotation right you'll be able to spot your landing almost immediately and time the rest of the flip.
These suckers are almost easier than regular backflips once you get the hang of them. Just make sure to pop hard off the lip and to look back with your head. And please, please COMMIT! Worst case scenario- you don't commit, you don't pop, you rotate slowly backwards while flailing and land on your head. Don't do that. If you commit to the flip you'll stomp it.
Once you get the hang of them, try switch flairs by looking over your shoulder when you pop backwards- you should start rotating.
'If there's a nipple, download it, then delete it.' - Matt Harvey