And this is HARD. And there's not really a thing (apart from having a guide to common abuse/manipulation tactics right there on your site) that I can recommend to every online community, they're all different.
One tip: make very clear that men, specifically, will be believed if they come forward with a report. Most progressive/leftist spaces take "Believe women" as a matter of policy, and that's great, but men are even less likely to report abuse and they really do need it spelled out.