There's two ways of twisting... one is through a pike and then straightening your body. The other one is generally used more which is using your arms to generate rotation. There's a couple of different methods but generally wrapping is the most frequently used. The one I use when I twist:
Left arm comes up to the shoulder like a biceps curl in hammer grip. Right arm comes to the left shoulder across the body. Pull with your obliques. If you jump and do this, it will start you twisting in the air.
The correct way to do this in the air is to have a good SET for your backflip (this is best learned out of a round off back handspring or round off) as you need power. Very few people can do standing back fulls, and you shouldn't try to learn one if you don't know what the hell you are doing. That's just asking for injury. Anyway, SET up with your arms fully overhead and your body extended in the rebound, then basically do the twisting motion I said earlier. It should take you around. A lot of it is just practice getting the feeling of your body twisting in the air and figuring out how to initiate and land it.
It would probably be a good idea to talk to a gymnastics instructor in your area and see if you can get a gymnast or gymnastics instructor to teach you IN A GYM.
