If you provide some of your interests/hobbies, we can probably be more helpful.
That being said, I think these are a few active and interesting communities:
Regarding places to avoid, I don't think anyplace needs to be avoided, per say. Politics can be problematic, if you go into those posts.
There's no real algorithm, so you need to curate your own feed. In general, I'd suggest, if you see a community that could interest you, just subscribe. You can always unsubscribe later (if it turns out not to be what you want), but getting a denser "good stuff" home feed is beneficial.
By the same token, I'd suggest blocking communities you have zero interest in (helps filtering, so you come across more content you are interested in when browsing "All"). If you run into a problematic user, report (if they have done something reportable), block, and move on.
If 2 communities are posting the same content and you get tired of seeing double, I'd suggest removing the community from the bigger or flagship instance (ex. Lemmy.ml, Lemmy.world, Piefed.Social).
This would have the effect of distributing the communities across the threadiverse rather than having them bunch up on a few. A problem with bunching can be if an instance goes down, they take their users/communities with them. Most of the medium/large instances in the threadiverse are stable, but it has happened in the past (Lemm.ee).
My understanding is this should be much less of a problem in the future, they are working on making user profiles and communities transferable between instances/servers.
Note: there is an active autism community, if that's of interest to you.