I am a retrained night owl. I used to work in the theatre which meant I worked funny hours, long shifts (often doing a matinee, an evening show then going to another theatre to do a night changeover, getting to bed at 6am then sleeping all day. When I started working on the web I would work late and generally not have great sleep patterns.

I retrained myself by starting to go to the gym or for a run really early (at about 6am) every morning. I just did that consistently until my body learned to have a pattern and I'm now very much a morning person, I usually get up at about 5am. The trick is to be consistent especially in the 6 months or so it takes to retrain your habits.