Best one I can give you is to simply twist your head in the opposite direction of the led you want.
So for left lead,
move your left foot slightly forward, right slightly back and twist your head out of the arena to the right (your body will follow just enough).
For right lead the opposite….
Move your right foot slightly forward, left foot slightly back and twist your head out of the arena to the left.
I had a 17’2″ warmblood with this problem. Once I did this he got it immediately. I got this from a friend who worked for a Grand Prix Dressage trainer. Worked for my horse so worth trying 
Good luck
