I assume you're talking about floor?
There are a million different ways of approaching twisting, and mine is but one. That said, here's how I teach it:
I teach an early twist (ie almost, but not quite, an arabian) and a late twist as parallel skills. When a kid is ready to twist, I have them working two drills. The first is to do a back layout and then immediate jump half turn (ie late twist). As they get comfortable with it, they can start twisting before they land instead of after. At the same time, I teach them a trampoline style twisting takeoff; I have them work, either on floor, tumble track or trampoline, spotted layout halfs with the twist comming straight out of the set. The idea is to set like a normal layout, but then instead of bringing the arms out or down to the side, one arm pulls back, pulling the shoulder and one side of the chest with it. At this point, you can spot the ground and either put the arms out (ie stopping the twist for a half) or pull the arms in (ie accellerating it for a full).
I don't think I'm doing an adequate job of explaining it here; it's easy to demonstrate but difficult to explain how I teach it. Perhaps when I get a chance I'll just make a video and put it on youtube.
ANYWAY, the two most important things are 1) twist over the top, not around the side. 2) YOU MUST BE COMFORTABLE IN THE AIR AND DEVELOP A GOOD SENSE OF AWARENESS. Admittedly you will get lost a bit as you're just learning to twist, but it's very important to teach yourself to use visual cues to know where you are as you twist. This is actually much easier with a full than with a half; in a proper full, you can see the floor for almost the whole skill, whereas in a proper half, you never see the floor.