"Playing" with the reins is basically using irritating little motions which cause the horse to duck away from the pain. It's not really engaging the mouth. The horse needs to be forward first and foremost. It is behind the rider's leg and is being worked backward (as in front to back). Try to put the foundation together first (forward, straightness, balance, etc) and worry about the head later. The head will come down naturally as a result when all the pieces are put in line and the rider's hands are steady and inviting. I hope that makes sense.