Make sure you can get the height for it.
Lean back, Pull back, Look back. Go straight over backwards, dont twist or go over your shoulder or anything.
Hold the FUCK on, if you bail and you stack its going to hurt twice as much more than if you stack and you hold on.
Lots of speed, and rotate slowly, you dont nead to throw your self backwards like a nun-chuk.
Get used to the feeling of going over backwards on like a trampoline or something like that, that helped me.
BTW i landed my first backflips to concrete today.