Great summary of best practices here!
Bob Durie

It’s always tough to deal with people pushing up against the norms, but generally having a set document of guidelines and having most everyone else follow them is a strong indicator people want to follow them. I would suggest taking people aside one on one to remind them of existing guidelines or posting guiding documents in channels as pinned items. You’ll probably want to shy away from shaming someone in a channel in public for not doing things the accepted way and continue tapping them on the shoulder to ask them to get in line with conventions.