Success Is Easy
Cues for the Flying Lead Change
  Keep in mind the cues are being exaggerated for demonstration purposes.  Once you are able to move the horse's hip with a simple shift of weight and leg position change, you will have much greater success if your cues are subtle.   The rider is sitting to the right and pushing the horse's hip to the left, then the rider shifts his weight to the left and pushes the horse to the right.  In the change from left lead at the lope to right lead, the rider makes a big weight shift to the left to demonstrate the cue change.  Watching from the side view, you'll see the rider's left leg move from a forward position  (horse is on the left lead) to a back position to push the horse's hip to the right, making the flying change of lead.       

Taken from the online course
Training Performance Horses