I did not write it but I keep this in my notes when I have such doubts ->
Circle of competence (read about it on wiki as well):
Short-term
What job can you be hired for an hold for a year and make the most money? If you forced yourself to make money doing one job and holding onto that job for at least one year, what would you do? What skills does that entail? If you're not sure, go network and interview.
What gigs can you get right now and get folks to pay you - whether you advertise on Quora, Facebook, call your friends, family, neighbors, etc.? What skills does that entail?
What do people ask you to do more than they ask others to do? That's what they think your circle of competence is. They're part of the market. The market will value your competence whether you like it or not.
Long-term
What do you like doing that is a marketable skill? What do you spend your time doing? You'll get better at something you like doing and keep doing, especially if that skill is in demand and others are not as devoted to it or as interested in it.
The things you do which you like doing and spend a lot of time doing - as long as you make sure you keep improving - will become part of your circle of competence.