Lots of great advice here!
If you work at a gym, I’d suggest that your first priority be to try and train a wide variety of clients to find out what interests you the most. Sometimes it’s hard to know what you like best until you try a few things.
My next thought would be, once you know what you like best, plus what you’re good at, is to develop a mission statement. The field is so large that we can’t be all things to all clients. Narrowing your focus to the areas where you have both passion and talent may help you build your career faster.