There are so many drills you need to master before trying a full twisting back layout. One of them would be this one I'm going to show you. This one is just a standing layout with a half turn to your back. This makes you comfortable with just a half turn, before you go and try a full twist.
Nice, it teaches your body to start the movement of twisting. The next drill is to do a running round-off back handspring layout with a half twist to your feet. Once you're comfortable with a half turn, you can then do a round-off back handspring layout half turn, and then jump into another half turn.
This prepares your mind for a full 360 degree turn. Once you become more and more comfortable you can start twisting just a little bit more and more and eventually you'll do an actual full twisting back layout. Those are the drills that you need to master before trying a full twisted back layout.