Sort of, I have a better idea of what it affects now. Basically each instance is a separate website, so probably the first thing you’ll want to make sure is that the server is stable and won’t shut down because then you’ll lose your account and any communities hosted there. Hopefully in the future you can migrate these things but currently that’s not possible.

Second, you’ll want to look at the moderation and federation policies of your instance. This will affect what instances you can access—federation is usually allowed by default but either instance can block the connection unilaterally. So for example, most instances have blocked a few far-right instances because they were posting some unpleasant things and not following the rules the rest of the community wanted to abide by.

Finally, for smaller instances especially you might want to consider the ethos and community of the instance. This isn’t essential since most of the time you can post anywhere, but it is nice to have that little community if you find a place of similar folks, and your voice may carry more weight on instance related decisions if it’s your local instance.

From what I’ve seen, sh.itjust.works is a pretty good general one, but unfortunately beehaw which hosts a number of pretty active communities has defederated so you won’t be able to access those. Hopefully it’s temporary since that kind of fragmentation I think is harmful when there are so few active communities right now. It might be worth checking out the communities on beehaw to see if you really want access to those, and if so you could make an account elsewhere.