Before you join a gym ...
40% -- that's really high, especially when you think about how many people have had memberships at the same gym for many years. if you join a gym tomorrow, the odds that you'll still be there in a year are slim. I have no statistics to back this up, but I have to think the main reason people don't renew gym memberships is because they don't end up going. There's a reason 60% of people are overweight.
So here's my tip for saving money on a gym membership: if you're seriously out of shape, a gym membership is not the first move. Try going for 2 long walks each day for a few weeks or months. If you can't commit to that, you probably aren't going to commit to going to the gym either. Fitness is extremely important, but there's no sense in throwing money away either.
If you are planing to join a gym, check out this video from the Dolans.