I think you can answer this question in two ways, based on what you are asking. Sue is giving you suggestions for what you can do with social media to showcase your skills, talents, experience, education and training. Martin is giving you suggestions for how to increase the things you have to showcase.
Both of these are important. Part of any job is developing a skill set, and part is learning how to present that skill set to its best advantage. My sense is that you probably meant the first, (and Sue has given some very good, simple, and effective suggestions) but it is good to remember the second as well.
I find Facebook can be less easy to use to advantage now that they are trying to monitize by charging to ‘boost’ posts, I am not sure if I were to pay for advertisement that Facebook is the first place I would start. It is a pretty good way to help develop community and share information about your schedule. You might also explore Linked In. I am not great with social media and do not really ‘get’ linked in, but people I know who are and do seem to get a lot out of it. Like this forum there is a lot of opportunity for discussion within the fitness community, which can be good.
Once you try a few things you will hone in one the ones that work for you. Long ago when I first started working in fitness someone told me ‘dig deep, not wide’. i think it is good advice. Once you find the things that work for you try to do them very well and frequently…. and don’t waste time on things you are doing just to get name recognition. People will be able to see when you are doing something because you are passionate about it, as opposed to trying to generate publicity. (Like the ‘like and share these cute kittens’ kind of thing).