Start off with the personal fitness trainer certification. You would need to become CPR certified also. Most all gyms and certification companies require this. Just starting off I recommend training in a gym chain for example ballys or gold’s and get used to working out in that atmosphere. By doing this you get experience and you have a client pool right there. You wont have to spend time searching. Then after you feel confident you have enough experience – the next step is opening up your own company. I would highly recommend doing it in that order.
another cert that is good is a business consulting specailist. It shows how to approach and sell yourself to all the different personalities out there. You could be the best trainer in the world but if you cant sell yourself – it doesnt matter.
The certification company I personally recommend is the ifpa. http://www.ifpa-fitness.com . I had an extremely good experince with them. Their materials are top notch. very practical in the real world……..I never have to go anywhere else for fitness education because any field I’m interested in – they have a certification for it.