Also: I'm starting a petition for a new IRC policy. (Not that it's democratic, but hey, petitions are good!)
If you have no idea what's going on when you join, then let the current conversation finish or at least wait until a good time before you try to jump in. As tertywerty hints at, it's quite irritating when there's a discussion happening and someone joins and immediately goes "HEY WHAT ARE YOU GUYS TALKING ABOUT".
Seriously, that's one of the surefire ways to get yourself kicked.