The place to start is to find out why YOU want to bike. For health? Lose weight? Sexy biker legs? Something to do with friends or family? Once you find your personal motivation, it's much easier to visualize the result and get up and go.

Personally I ride in the morning before work, and sometimes it's tough to get out of bed and get right on the bike, especially those 30 degree winter mornings. My motivation is fourfold:
1. (guilt) my BF is waiting for me to meet him and if he bothered to get out of bed I'd better too
2. (vanity) upcoming wedding photos
3. (health) the bloodlines want me to be a bit ... thicker ... than I'm comfortable with and it's a constant battle to stay in my size 8s.
4. (competive spirit) a lot of friends are quasi-competitive athletes -- rowing, cyclilng, marathons, tri's, skiing -- I like to keep up

Anyway ... it works for me.