Steve Pavlina has two posts on how to consciously alter your sleep patterns. I don't agree with him about everything, but these are at least good suggestions to try.
Like Steve, I go to bed when I'm tired and typically fall asleep very quickly. Recently I have found myself waking up before my alarm. Like Steve I get up at a predictable time on work days but unlike him I do allow myself to slack off a bit on the weekends. Those extra few hours of sleep are a treat I give myself. I wonder if they aren't doing more harm than good to my sleep cycle.
I do not agree with him about reading in bed in order to cool your brain down and prepare for a sleep cycle. A good book will keep me awake and reading for hours. A bad book will piss me off and keep me awake as well. I know Amybear is the same way. Reading makes me think and generally encourages my brain to keep moving. Another great way for me to have a bout of insomnia is for me to go to bed and have a neat idea there before I fall asleep. Unless I can put it out of my mind for later, I'll be stuck mulling that concept around in my head for hours while I stare up at the ceiling.
What I really need to work on is getting up. As I said, I typically wake up before my alarm on a regular basis. However I always roll over and sleep until well past when the alarm goes off. I suppose I just need more self-discipline, but that's the story of my life.