Sharky - the way I do it is to DO IT.
I am THE laziest person for doing stuff I hate. I can practise my guitar or do my Kung Fu for hours, but work - I'm f*cked.
The trick is to DO IT. Stop thinking. Just open the book and start.
Really.
If I think about it I find myself negotiating between the part of me that wants to stay on the couch watching KISS waiting for Beyonce or Holly to come on, and the part that wants to pass my A-levels. The trick is just to force yourself to work. No conning yourself that "5 minutes won't hurt" or "As soon as I'm back from the pub". That fails.
Unless you're a guy who can do excellent time management, this is the only way. Trust me.