The easiest thing is to do what you know. Find a problem you have, and probably others have that problem too - though then it's a matter of finding if there are any worthwhile solutions already existing for it. Even if there are, maybe you can build a better version?
What are you goals? Long-term recurring revenue? Want to make $50,000 a year? $500,000 a year? Etc..
Short term goal, is to learn how to get people to pay me. Long term goal is to quit my job with in the next 1-5 years, and taking in my current salary from my own company.
You have a long run-way, so that's nice, though markets change - so you have to try to be a bit of a seer ...
a) Join a startup you could learn about / be part of marketing, while being paid to do different work than marketing
b) Learn about different business models in the meantime, along with how marketing works. Books on copywriting, marketing (Influence), etc..
What are you goals? Long-term recurring revenue? Want to make $50,000 a year? $500,000 a year? Etc..