If its exercise motivation you're looking for, the gym isn't always the answer. finding a sport that actively requires you to turn up is always quite a good place to start. For me this was boxing, as i was trying to make a squad that, were I not to turn up to training, I wouldn't have made. But team sports are a good example, as they push you to go even when you dont want to, as you ruin the experience for others if you don't. the best example ive seen is rowing, as people cannot go out unless they have everyone there (although that's a pretty difficult sport to get into). Other examples would be finding opponent sports, like tennis, badminton, squash (one of the best workouts you can have!), for which you have a regular partner to play against. a lot of clubs can be quite cheap, and often run ladders that mean you'll always have an opponent to play. Plus, team sports tend to keep interest for longer - they're more fun in my opinion than operating alone in a gym.
friendly competition that is.