Back in the day you could get away with being a jack of all trades. Now, as all sub-niches are getting so specific, ideally you choose a type of service and just go crazy deep into specializing yourself.
I used to do web design (well, still do), am more than competent in forum management, graphic (logo) design, CRO etc. But I have specialized myself in SEO and in the past years this has been my main occupation.
As soon as you get seen as an expert, you can demand better prices and be able to provide a top-service.