How long have you been thinking about starting a new diet or fitness routine? For me, I spent almost a year "considering" exercising before I finally got things moving. As my mid-section continued to expand, I made excuses about work, time, family commitments, etc. Sound familiar?
Most people need to find their "passion reason" for working out -- the emotional motivator they need to stick to their fitness goals. You can find your own "passion reason" by making a list of things that are important to you -- your "power list." By jotting down a few goals, and ways in which you'll achieve them, you can find the justification you need to lace up those running shoes and hit the pavement (or the gym, or wherever you go to keep active).
Now that I've found this, I think I'll re-evaluate the "passion reason" that got me started, which was, essentially, to avoid public embarrassment. When I started running, I told the readers of my personal blog that I'd post before and after pictures of my gut. While I've definitely made some progress these last couple months, now that the deadline is approaching, I may have to renege on that promise.
Need ideas for your list? Jorge Cruise makes some great suggestions here.