Hey admins! There are many ready-made collaboratively-built instance blocklists on the Fediverse which you can use to protect your users from trolls and abusers.
Probably the easiest way to discover these lists is on the Oliphant.social page about them, with links to a dozen different lists:
https://writer.oliphant.social/oliphant/the-oliphant-social-blocklist
Each list has its own methodology, usually involving a group of admins voting. There are also blocklist subscription systems in closed beta testing.
@homegrown oh! I'd thought Oliphant had stopped updating that, but it's recently updated, and the methodology is slightly different. Thanks for the reminder!
There are also links to many other people's lists on the same page, so if one list doesn't work for you there are alternatives