My one-tweet Mastodon starter advice:

1. Pick a server where people are likely to post generally about stuff you're most interested in.
2. Follow interesting people on other servers, who will boost interesting stuff into your home feed. THEY are your algorithm.

@garius Ive signed up for 3 different servers at this point, and they all seem to be either general, geography based, or specific, VERY specific niches. I hope this expands over time, or otherwise I don't see the point unless you want to box out the crowd intentionally.