Position, position, position. Not heals down, legs back, shoulders up. Precise placing over every hoof that touches the ground. My hip moves off of the line a millimeter he should respond. My pelvic bone tilting any way should cause him to respond, sending him flying forward, or slowing down. It's more than walk, trot, canter. It's every little thing in between that I need to pay attention too, otherwise, in three little things, you have a big thing.