Hi I am new here but I think I can provide some insight. I have a personal trainer. The very best part of the whole arrangement is the accountability. Left to my own devices I can find a thousand other things that I need/want to do. But when you know someone is at the gym waiting for you well... you gotta go.
I started by getting references from some of my friends. I really wanted someone who was well versed in all areas cardio, strength training, nutrion, flexibility training.
When you are interviewing them make sure they are taking an active interest in your particular situation. It's great if they know alot about exercise and fitness but it isn't going to do you any good if they don't listen to you enough to develop your personal program.
Be sure to talk about their fees on the front side. If you end up with someone who is affiliated with a health club find out if their fees include the use of the club or if you have to pay seperately for a membership.
Also, find out if they have liabiliy insurance.
Oh, and make sure they will work around your schedule and not vice versa. It is very important that you set yourself up for success. You don't want to feel like exercising is a burden because you have to squeeze it in based on someone else's availability.
You might even ask them to tell you about a typical week's routine. That will give you an idea about how they incorporate cario,strength and flexibility training.
I hope thats helpful. Good luck finding a great trainer. Nancy