I think you have to want to do it. I tried the gym in college, I tried doing things on my own after college, I tried the wii fit and other things after that. Once I finally decided that I wanted to get in better shape and decided on a schedule I knew I could do it was easier. Feeling better once your done helps too. My back can be cranky from sitting all day and after a run on the treadmill after work it feels better.
After almost 4 years of going to the gym and doing a couple of races the past few months, I now get irritated when I can't go to the gym because something comes up or I don't feel well. Don't get my wrong, I do still purposely skip days and I built in a skip day every other week because I knew if I didn't I would burn out and skip more often.
It's all what works for you and sometimes it takes more than one try before it sticks or more than one motivation tactic before you figure out what works for you.