First things first. You can't ride a horse you can't get close to. Be in the stall in a non-threatening way, but don't get pushed around either. Have a rope or stick with you and if the horse turns to you, stand there or pet him depending on location. If he turns his butt to you, swing the rope at it or tap with the stick. Be careful as he may use his feet to indicate that you need to move. You will have to LEARN position, timing and feel. You won't be good at first, so approach it as a lesson for you and the horse.