Having seen what a huge proportion of new users create an account and then just never seem to do anything with it, I really believe Mastodon needs something like starter packs, and maybe even a little automated thing that offers a few upon signup (this part could be managed by instance admins, rather than universally). Follow lists are ok but the mechanism for importing them needs to be simplified a lot, like "click this button" simple.
The one big thing I would change is that people should have to grant permission before being included in someone's recommendations.