There are a few rules that you should keep in mind while on IRC. After all, it IS a world wide network, and there are real people out there. A lot of people disregard some of the common etiquette on IRC, but we going to list it anyway and hope it serves as at least a little bit of a guiding factor.
First thing to keep in mind is that while English MIGHT be the most widely used language on Internet Relay Chat, it is not the only language. There are some channels that restrict the languages, and others that just don't like foreign languages spoken. Try to keep that in mind, especially if traveling to channels like #france and #germany and #espana and other foreign channels. They are nice places however if you might want to practice a foreign language (or speak your native language).
Another thing that CAN be annoying is to come on a channel and greet everyone on the channel you're joining. Some channels don't mind it as much as others, but when people join a channel and all you see Hi this person, hi that person, it can be very annoying. But being friendly is a part of IRC, so if it's with friends, and the channel accepts it, you can go right ahead and do it.
Another annoying thing is ops begging. Many channels can't stand op beggers.
Ops begging is a comment such as "ops please?" or "can I have ops?" and "opme pleez?" All these comments could get you kicked from a channel if you haven't been around that channel very long. I know I don't like it when a person comes on the channel for the very first time, and within 5 minutes is asking for ops. Just don't give ops to people you don't know, also never op new people on the channel. If you want to be courteous, wait until you make friends on the channel, and ask them for ops. If they give it to you, great. If not, don't worry, you'll get ops one day if you have patience.
As for conversation on IRC, keep in mind that the only thing people have to judge you by and form opinions from is your words. Some people don't care what they look like on IRC, since they consider it a game. Others take it more seriously than they take their real life.
In your exploration of IRC, I can guarantee that you'll come across both types if you hang around IRC long enough. Basically, my philosophy is to try to be yourself and enjoy yourself on IRC. I try not to take people too seriously, partly because not many people take me too seriously.
Some general other things that are discouraged on IRC, and could result in being banned from a server, or even harsher actions, depending on the severity include:
"Harassing another user -- Harassment is defined as behavior towards another user with the purpose of annoying them. However, you might note that because of the ignore command, there is very little done about harassment.
"Annoying a channel with constant beeping -- Action sometimes is taken if a person does this consistently, mostly because it can start to bog down the server if it persists. That is part of why some war-scripts can lead to a user getting himself banned from a server.
"Any behavior reducing the functionality of IRC -- Basically, if it is something that might result in IRC being less then it is, it's a bad idea to try it. Pretty simple :)
Keeping these guidelines in mind, you shouldn't have too many problems on IRC. But there are always people who start things, so just don't get flustered by other people, and try to stay in the spirit of Internet Relay Chat, which is....to Chat. :)