Well, it depends on your ultimate niche, what you love to write and for which audience, and then you join a forum that is focused primarily on that.
In my case, all of my story commissions over the past 20 years have come from "furry" sites, such as Furaffinity and SoFurry, and I actually started out the same as anyone else - I shared my work on the site, people started to read it, loved what they read, and requested other ideas.
I've been extremely lucky to get repeat customers all those years too. They helped me out with unexpected expenses often; even helped me keep my house payments going for two years. So, yes, just decide what you really love writing the most, join a massive forum reflecting your interests, and share your work with others. People should notice and begin asking you to write something else.