What are common IRC rules and etiquette?
For starters, be sure to check http://www.atrum.org Additionally, it's good to keep an eye on the Message Of The Day that is displayed each time you connect to Atrum If this is not displayed, typing /motd should show it.
Further to the above, most channels on IRC, in general, have the following rules:
Do not speak in CAPITALS.
Do not flood other users or the channel.
Do not have an 'auto greet' script that greets anybody as they join the channel.
Do not harass other users.
Do not use colour.
Again, this depends on the channel in question. Some may have more rules, some less, and some very few ones may not care at all. It's best to ask one of the channel operators if you're unsure. These are the guys with "@" signs next to their nicks.