Groundwork-let the horse know you are the boss. Don't be harsh, just make sure the horse knows that you are the boss.
Try this: bring a flag (parelli carrot stick w/flag on the end) or crop/whip into the stall. If the horse tries to crowd you, just give him a tap. If he does not listen, tap him again, a little harder this time. Also, when you are leading him, hold a crop/whip or flag in one hand. If he trys to run ahead of you, tap his chest. If he tries to push into you, poke him in the shoulder.
This does not hurt the horse! It is just teaching him manners.
I do this w/ my horses and they are very respectful with me on the ground, and also in the saddle.