Have people expect your writing.
This is another reason blogs are fantastic:
if you build up an audience, you feel the pressure of their expectations.
This pressure is a good thing — it keeps procrastination from taking over your life.
You know the audience expects you to write, so you get off your butt and you do it.
From Dan: That last point? That’s what a critique group does for me more than anything else. Motivates me to post a chapter or two every week.