'Pop-off-the-wall' is an excellent exercise to develop a quick rotation off the box. The fastest turns I have ever seen were a result of the dog using its front-end effectively as well as its hind-end rather than relying on its rear legs to torque its body around.
Classical conditioning or associative learning, a click is best for accurately marking a correctly performed task. It begins by teaching a dog that a reward follows a click, so click then offer food, pause and repeat.
Operant conditioning or instrumental learning, a good activity for a dog starting to learn clicker training is teaching your dog to touch the end of a stick. When the dog touches the end of the stick you click and reward. For this you could also use a 'YES' if you don't already use a clicker. Be patient and don't put the stick in front of the dog's face, wait for the dog to chose to come to the stick. A quick way to get the dog started is to rub a bit of food on the end of the stick. If the dog is going to turn right, the stick and clicker are in the left hand, food is in the right. If the dog is going to turn left, the stick and clicker are in the right hand, treat is given with the left hand.
I want my dog to use its front legs to rotate since I'm trying to develop the front end push and strengthen the associated muscles. I don't do too many repetitions at one time to avoid over-stressing the joints. I prefer to switch over to a tug once I can stand back and send my dog since this develops more speed in the rotation than coming back for food.
Add distance by using body language to develop a 'send'.