keep in mind you aren't going to make much money at first, especially if you work at a franchise gym. the key in my mind to being a great personal trainer is LOOKING the role first off. none of the personal trainers at my gym even look like they lift, and as a salesman I do not see how they are going to be able to gain and retain clients. so look the part first and foremost.
I know musky is a certified PT, i'm sure he will chime in soon to give you some advice on what he recommends