This is more so contest specific than general tip, but here it goes.
Post your before pics when you start the transformation. Taking the pic is one thing, but actually posting it takes it to a higher level. I think this is one of the biggest challenges that we face. It hurts to do, but it makes the contest entry more "real."
For me it seemed to make me feel more committed when I'm showing my actual picture. My attitude was that well this picture is out here now, there's no turning back.