This past Saturday I woke up in the Flow. Basically speaking, Flow is the state of mind where you are fully immersed in what you are doing, to the exclusion of the outside world. There's been a lot of research and discussion on this topic, which I won't go into simply because I'm too lazy and it's already well-documented in this Wikipedia entry.
Anyway, I got out of bed way earlier than I intended to because there was a melody swimming in my head. I rushed over to my guitar and searched for a chord progression that would fit under that melody. Once I found it, a chorus immediately suggested itself and I started working on that. To my dismay, after I nailed down the chorus, I found that I had forgotten the original melody that inspired the whole thing to begin with (when this happens, I try to make myself feel better by saying, "If I can't remember it, it must not have been that good in the first place.")
So I came up with a new verse melody, and "Sad & Glamorous" was born. Being still in the Flow, I finished up another song that I had been working on (using some riffs from Dan), and that became "Burn." It felt like only a few minutes had gone by, but after I was done, I realized that a couple of hours had passed and I hadn't eaten breakfast or taken a shower or done any of the other stuff that I usually do when I get up. We ended up practicing both songs that afternoon and playing Sad & Glamorous at a show that night.
I love being in the Flow. Mostly it's a state that just occurs randomly, and the conventional wisdom is that it cannot be forced. But I think that as far as creative endeavors are concerned, you can prime yourself for possible Flow entry by simply staying creative - write or play anything, no matter how silly or stream-of-consciousness it may be. Write aimless blog entries about what you did on Saturday morning. Read books and listen to music to gain inspiration. I had spent time the night before thinking about plot details for Book Two, and I believe that doing so led directly to my Saturday Flow experience.
Just don't forget to shower before you head out the door.