It's easy to work out consistently for a few weeks when I find a new workout program that I'm excited about. What's hard is continuing to work out after the program is over, unless I have the right motivation.
A nice body is definitely motivation to exercise, but for me, it is not very effective. Perhaps that is because I'm always wearing a huge coat (I have little tolerance for even slightly chilly weather), and it really doesn't matter what's underneath the huge coat. When the alarm wakes me at 5:30 every morning, I get up to go to the gym not because I think, "it's time to improve my physique."
Instead, I play two scenarios in my head:
Scenario 1: I don't work out. Work is stressful and something upsetting happens.
Scenario 2: I work out. Work is stressful and something upsetting happens.
What happens in each scenario? I'm sure you can guess. The difference is in my temperament and how I deal with difficult situations. I feel a greater sense of calm and control in Scenario 2. When things around me go wrong, I can breathe deeper and feel less crazy. Of course, this is all in my head and I'm sure in real life, the difference between Scenarios 1 and 2 isn't quite as profound. But time and time again, I prove to myself that a morning workout results in a happier me for the rest of the day, even when I feel miserable for the first hour.
As a bonus to this mind game, I also visualize the sweaty walk from gym to car when I'm done with the torture. The unusual sense of accomplishment for something as insignificant as an hour-long workout pushes me to go back (almost) every morning, and when fitness becomes a habit, then it really is a significant accomplishment!