How can I tell if the fitness club I'm joining is right for me?

Did you go back? A good fit is a club that has people with whom one wants to associate, instructors with good reputations, equipment that is safe and available, etc. Paying a high price for a fitness club membership is a potential motivator, but it is important these days to find a center that one can afford over the long run.
Individual feel. First - think about what you want to get out of it. Some benefits are: aerobic fitness, muscular strength, comradererie, etc. Different clubs may offer fitness classes or racketball, etc. If that is your thing. Other people just want really good weigh equipment. Some people want trainers. Get a feel for the different clubs in your area and see what works best for you individually and the cost.