What is the best way to teach your horse flying changes

My horse's old leaser started teaching him but never got the chance to finish, im not sure exactly how far she got so i just want to start teaching him from scratch.

The most common way is to start cantering on the correct lead (so for example, left lead when travelling counterclockwise), go across the diagonal, and then when you are approaching the corner, bring your left leg back as if you are asking for a canter depart onto the right hand lead as you begin to travel clockwise.

Some horses will do it automatically at that point, as they sense the change in direction and balance, and are also prompted to push off into right lead canter by your leg aid.

It takes a sort of definitive leg aid and also a shift in your body weight to really induce the horse the switch leads in this way.

Make sure you are cantering nicely forward (the horse needs momentum to push off and switch his leads). Being in a half seat or two-point position also helps the horse to use his back.

If it doesn't happen automatically, repeat the pattern (going down the diagonal) but instead of asking for a flying change, do a simple change of lead (by coming back into trot and then picking up the other lead.) Do this over and over until the horse starts to anticipate the simple lead change. Then try just leaving out the trot part, and using your leg aid to ask for the new lead. Most horses will understand at this point that they are supposed to get onto the other lead. If he tries to break to trot, try it again but with a more forward canter. The horse is understanding at this point he is supposed to switch leads but hasn't sorted his legs out yet. Just keep trying and don't get upset - if the horse gets nervous about flying lead changes, it will make it all that much harder to get clean changes!