Follow people and hashtags and interact with them and you'll get followers. I barely post, just a few replies a day, and I have over 800 followers. I have a pinned post on my account to that effect.
I would join mastodon over bluesky because bluesky seems to be on the same mesh it to fixation trajectory as any other VC backed social network. But yeah, I get that most people won't see that for another couple of years... Oh well. At least people are bailing twitter. And when bluesky goes to shit mastodon will still be there, and the rationale should be a lot clearer.