Have an actual mission statement beyond just being a general purpose instance (e.g Beehaw, my instance, most of the topic-based ones, etc)
Replace the default frontend with anything better than Lemmy-UI
Building on #1, try to curate the experience into something positive.
Block the toxic aspects as best you can by default. Don’t make new users discover and deal with the toxicity on their own. There’s plenty of other general purpose instances that will let people rawdog everything (and everyone) on the Fediverse if that’s what someone wants.
Focus on “quality over quantity” and block all the content repost bots / defed from the instances that do nothing but repost Reddit content. Disallow AI slop in all its forms and focus on human interactions.
Consider hiding/disallowing Politics communities and don’t allow accounts who post with an obvious agenda.
Systematically Identify and ban accounts that do nothing but downvote (if everything here displeases them so much, perhaps they should go elsewhere, ya know?)
Clean up duplicate posts; even if they’re slightly different, seeing the same story posted 10 times gets old for users.
This is a great list.