Goto local meetups, reach out to local businesses, start a blog and contribute to open source projects.
If you’re interested, I elaborated on some of the above tactics in this article: https://nickjanetakis.com/blog/how-to-start-a-successful-freelance-business-as-a-software-developer
I definitely wouldn’t bother with freelance market place sites. If you’re curious on why not, here’s a quote from the article on why freelance sites are comparable to Dante’s 9 circles of Hell:
“I should spend a large portion of my life to become an expert in my craft, and then I should agree to have my privacy stripped away from me while I race to the bottom and undercut my competition because I will actively place myself into situations where I have the highest competition to ensure I receive the lowest rates. Lastly, I will bust my butt and bend the world to satisfy clients who take advantage of me.”