To become a personal fitness trainer, you need to have a multitude of skills. You should be patient, persistent, nurturing, an effective motivator and a good listener. You should then choose an organization that is nationally recognized and accredited. Go to http://exercise.about.com/cs/forprofessionals/a/ptcareer.htm for more details.
I would look up jobs for personal trainer and see what the potential employer is looking for. then find a way to build up those skills. you can do formal study - get a degree. there is also informal on the job training - start in a low job, learn the ropes, and then try for a higher job
Do you have an YMCA where you live? My cousin works as a personal fitness trainer there and didn't have to go to school for it. I imagine she just does basic stuff and she said she would get paid better if she did go to school for it but just for starters you could get a job at the Y in the fitness area for experience.