I built very simple tool in an industry that I wanted to be part of and was surprised to find that a few people wanted to pay for it. I mean very basic - done in three days.
A few months improving that and soaking up everything I could find (newsletters/press/blogs) led me to noticing a larger opportunity in the same industry so I built that and now it supports me full-time.
So I would advise picking an industry or niche that you're interested in (preferably one that's growing and not particularly tech-savvy) and then spend some time reading up on what people in that industry talk, write and complain about. There are opportunities everywhere.
A few months improving that and soaking up everything I could find (newsletters/press/blogs) led me to noticing a larger opportunity in the same industry so I built that and now it supports me full-time.
So I would advise picking an industry or niche that you're interested in (preferably one that's growing and not particularly tech-savvy) and then spend some time reading up on what people in that industry talk, write and complain about. There are opportunities everywhere.