It started with the blog post in my pinned tweet. That made it to the frontpage of HN and got me my first ~2000 followers in a week. Then I kept sharing details about my business and self-employment journey. Occasionally a tweet goes a bit viral, and it gets me a few hundred followers. But most of the steady state growth happens from other people recommending me to their followers. In the course I just released I go in a lot more detail about what I did, and what I've seen work and not work.