Recognize your personal space, and make sure he recognizes it, too. Practice driving him out of your space and having him just stand there nicely, out of your reach. He gets left alone if he respects your space, his world ends if he invades without your permission.
I've heard the same thing about eye contact being an aggressive form of body language, and I do use it sometimes. Although, I also differentiate between "soft" and "hard" eyes, if that makes sense. Soft eye contact is okay, it just means that I'm looking at the horse's head for whatever reason. Hard eye contact is part of the whole nonverbal "get the heck out of my space" phrase.
I like backing up a lot - my horse has had a pretty good education about this, but sometimes he does forget himself. If he even starts to edge into my space without permission, my first correction is to back him up with energy.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown