I haven't had time to write a real thing but I'm seeing a ton of new people, so here is my quick/dirty advice for people just arriving:
1. Just use the website at first. Third-party apps are great, but they often lack important features and may act weird when server loads are high, which they are during big migrations from Twitter. I started understanding a lot more when I switched to the web version.
2. Picking the right instance matters, but not for the reasons listed in most Mastodon documentation! Topics matter much less than filters you want applied over the gaping maw of the unmoderated internet.
Assuming you do not want to live your new life on the federated equivalent of 4chan, pick an instance with clear, strong mod rules and a nice big blocklist to keep the nazis and trollfarms away. (You can find this stuff on the About page for most servers.)
3. On server rules: If you don't want to share space with assholes, picking a server with rules like "Free ThinKers 4 Life, no snitching, the end" that will not go well for you.
A well thought-out set of rules/code of conduct is often a sign of thoughtful, engaged moderation, which is what you want.
4. On blocklists/defederation: The better managed your instance's blocklist, the fewer racists, transphobes, and other jerks you will need to pick out of your teeth.
Once your instance defederates from, say, a trollfarm, the people on the trollfarm can no longer see or interact with the users on your instance—and you won't see the trolls at all either. It's super nice! But your mod team needs to be proactive about it bc the trolls are always making new nests.
5. It truly doesn't matter if your friends are on one instance and you're on another *unless* one of the two instances does something that gets it defederated by the other.
Usually defederation is used to throttle abuse, but some instances are aggressive about defederating from any instances that break their social norms. Can this be finicky and stressful for newcomers? Yes!
For many reasons, it may take you a few tries to find a place you really like.
7. On citizenship, once you're settled in:
Support your mods/instance owners financially, if you can.
Take the time to write alt text for your images.
If you write about controversial people/topics, use the actual words so that people can filter your posts if they want to.
Consider not telling other people who have had unpleasant experiences that you are not having those!
There are a million how-to threads around, so I've just tried to focus on the parts I don't see discussed as frequently in places where new people are looking.
Loads of detailed advice here: https://github.com/joyeusenoelle/GuideToMastodon
Please feel free to recommend open servers with great moderation in comments!
<3
@bruce @kissane the list of servers that mastodon.social blocks is a good start. https://mastodon.social/about
See "moderated servers"
Thank you both. I'm still learning. I run a tiny instance of my own and my resources are consequently few. This helps.
@arranrp It is! But you can't take your posts with you—you open a new account and then migrate your follows and followers following a slightly arcane but googleable process I won't attempt to summarize.
It's clunky, but not difficult.
Or build your own. I did.
@kissane thank you for all the information. I’m new here and trying to get my feet so this is helpful.
I was just telling my husband tonight how I love the feature which recommends adding descriptions to your pictures.
I’m looking forward to settling in.
Erin Kissane
Auntie Denier
Bruce Heerssen 
David Andersen
Arran
Iαn has moved account
Tom Parslow
Futurist Jim Carroll
Steelerfan4lf3
Nerissa