I'm actually seeing some folks here sticking around from BlueSky after yesterday, so I decided to write a little mini-guide to Mastodon emphasizing points I think are important. I'm sure there's other stuff but this is what came to mind and could fit in one post:
1) There is no algorithm here. Everything is displayed in chronological order and your feed is self-curated. In other words, you have to be the one to make things appear in your main ("Home") timeline. You may only be stumbling upon this post because one of the few people you follow boosted it. So you know, there are multiple timelines to choose from: Federated feed (which I do not fully understand how it populates but I think it has to do with your follows and followers), your "Local timeline" which is other users on your instance, and a followed hashtag timeline which I don't personally use but you can ask others about and they'll happily answer. Speaking of which:
2) There is no shame in reaching out and asking for help if you don't understand how Mastodon works. We get it, it's weird and confusing at times and we like to see y'all stick around, so we're happy to offer the tools you need to make that comfortable.
3) Some users will refuse to boost things unless you add something called "Alt text" to images, which are image descriptions. This can seem very intimidating at first because you'll see photographs with elaborate detail that you might not feel you can /possibly/ replicate. In actuality, all you need is a basic description: "a drawing of an anthropomorphic cat with brown fur smiling and waving" is all you need to get the point across. The reason we all care so much about alt-text isn't only that it helps users with sight impairment. It can give context to a joke, it can let someone enjoy an image when they have a slow connection, and sometimes it lets someone else actually understand what they're seeing, among other things. If you're an artist who's trying to get their name out there, alt-text /will/ make a difference. And along those lines...
4) You will probably not get as many followers as before in terms of sheer numbers. The numbers themselves won't be as large because unless the other major social media sites go down, Mastodon and the Fediverse in general aren't going to be as populated. It can be discouraging to have to go from like 10,000 to maybe 200 or so. The trade-off is worth it: you get a lot more genuine interactions and a /lot/ less trolls and -phobes. Yes, there are some bad actors but that's unfortunately the case with everything, but the difference here is that you can actually report someone and expect something to be done about it. That said: your numbers will go up over time, it just usually takes longer than elsewhere.
5) A lot of people here like to babble about tech stuff and you might not understand any of it. Let them babble and know that if for whatever reason you're having a tech issue you /will/ encounter someone who knows how to help you. You'll also possibly encounter someone who's a snobby tech-twat and ridicules you for it, but I'd argue there's a risk of that happening everywhere. If you encounter someone like /that/ just block and try to move on with your life.
Mastodon isn't the only part of the Fediverse, there's things like akkoma and sharkey but Mastodon's the one I'm most familiar with. The nice thing is that if you're not happy with where you're currently located instance-wise, you can migrate somewhere else without much difficulty.
Hopefully this helps!