1) No spamming. Duh. Don't join just to ask for LiveJournal codes or whatever. There are separate communities just for that purpose.
2) No bashing. Don't join if all you're gonna do is complain about how Cartoon Network is "ruining" anime by editing it. Also, don't bash someone else because their opinion doesn't agree with yours. An intelligent arguement is one thing, saying "DBZ ROX!!!1111" is another.
3) No Adult Swim stuff. This is called the Toonami Community for a reason. There are other places to talk about Adult Swim. However, if you are talking about a Toonami vet on Adult Swim (Such as YuYu Hakusho, Tenchi Muyo!, Gundam, or Outlaw Star), then that's acceptable.