It may be helpful for you to find a mentor, someone in your area who is currently a trainer who you can both shadow and ask questions as you go. Will you train at a gym, in your home, or someone else’s home? Do you have your own equipment? Just a few questions to think about. You definitely need liability insurance if you will be out on your own.
Making some connections in your area is also helpful–and you could even do a few informational interviews with other trainers or fitness directors to give you a better idea for what you need to start your business.
Best of luck to you,