Keith pointed out a good distinction, which I heard phrased once as,
We are either pulled by motivation, or pushed by fear.
I'm not a huge fan of fear, but it sure does work sometimes.

So, why not use both?
1. Set up some external deadlines, in addition to the ones you mentioned. (You could say to a friend, "if I don't show you my work, completed, by Friday, I buy you dinner." Or something similar that works for you...)
2. Find out what your passion is for doing what you do. Write it down, post it on the wall, make a t-shirt out of it, whatever - but remind and reinforce your passions.
And pray. That's always a good one.