Before you begin any tennis program, find out if you are able to interview with the instructor. Get a feel for what they can teach you as well as if you do like them. If you are unsure, you wont be able to actually find yourself playing the game as well as you could be.
When signing up for a tennis lesson or tennis school, find out how many people will be working with you at the same time. For example, do you work alone with the instructor or do you work in a group? The more people that are in that group the less likely you are to get individualized attention.