I really like Kelly's idea of formulating a new lifestyle being compared to learning a new dance.
I had no idea how to live a healthy, active lifestyle when I was first getting started, because I never had before. So I've kinda approached it one step at a time. First was to overhaul the eating. I stuck to my eating plan like glue, only veering from it when I had given myself prior permission (Christmas day, eating out one day on vacation, very few times). I made a declaration to myself that THIS is how I am going to eat, and I stuck to it, I really did. I could give myself a big hug for that, because we all know how hard it can be, but sometimes you just have to draw a line in the sand.
Once all that really started to become habit and well ingrained, I moved on to incorporating some exercise. I could still definitely step it up in that area, and have fitness goals in mind. Thing is, the better I feel from eating well and having lost some weight, the more I just absolutely WANT to move my body in pursuit of fun and fitness. It's only getting better and better!
I quit smoking about 11 months into my lifestyle change, because I couldn't rationalize it with this fit and active lifestyle I am pursuing. Next step, I haven't been to the dentist in a couple years because I'm absolutely phobic about it -- so I'm going to get my dental/gum health in order next! One thing at a time and I am slowly moving from the least healthy person I know to one of the healthiest!
I think the bottom line, like a lot of people have said before, is that you have to be so fricking sick of living the way you are living that the excuses just no longer hold water. That is what happened to me. I felt so awful that I simply could not continue with my old ways. Unfortunately, I don't know what one person can say to another to make that click happen. But keep working on it, I believe if I can keep moving in the right direction, anyone can!