Two things: try not tilting your head when you come to full draw, and try using a Formaster. I don't think tilting your head necessarily has anything to do with collapsing, but I've been taught that it's just better form to keep your head still and draw the bow to your head. I can guarantee you that if you use a Formaster, it will be obvious to you if you are collapsing or not, and it has helped a number of people to overcome this problem.