This question is very often asked. There are two main things:
- Be active in the community. Talk to other people. Play their games. Leave feedback.
- Use social media, have a website of your own outside itch.io, and promote it.
Just don't try to act like the marketing department of a big publisher, because people are fed up with that. Plus, they can see through bullshit.
Be there. Be a person. It's not easy, but there are no shortcuts.