Communication is one of the most important factors on all raids. There are several channels that we are using and each of them is used for a different purpose and by a different set of people.
The /rs channel is reserved for the most important messages - especially instructions. There are only a few people who should ever be using it: the raid leader to give instructions, raid assists to call assist on monsters, the pullers to notify the raid about incoming monsters, loot captain to call information about loot, sometimes casters to let the raid know that an important spell has been cast (especially mez and some debuffs), and a few more. /rs should never be used for general chat.
dofraid is a channel made for general communication about the raid. Ask questions in this channel, put your Hello's, congratulations, etc. messages in here, and so on. Even though this channel can be used for anything, please try to keep the discussions that are not related to the raid to a minimum; the less text the sixty or so people have to read, the less likely it is that someone will miss important information in the other channels.
dofhealer is the channel that we organize healing in. All druids and clerics should join this channel when the raid starts, sometimes the healer leader will ask other classes to join as well (mostly shamans and necromancers). Healing strategy is discussed in this channel - from CHC through AE heal chains to rezzing.
doftank is the channel where tanks discuss the strategy for the raid. All plate tank classes should join this channel on the larger raids, sometimes other classes (especially enchanters and non-plate tanks) will be asked to join this channel as well. Tank order, offtank list, and other things related to the tanks are discussed here.
dofchanter is the channel where enchanters discuss the mezzing strategy, buffing, and other things. All enchanters should be joining this channel. Sometimes the enchanter leader will ask bards to join this channel as well.
shambles is the channel where our shamans discuss buffing strategy, delegation of debuffing duties, and so on. All shamans should join this channel.
dofpull is the channel where the pulling teams communicates. Usually only the delegated raid puller, raid leader, and raid main assist join this channel, but sometimes the puller will ask other people to join as well.
Sometimes using all of these channels does not make sense on a particular raid - especially on smaller raids. In such a case, some of the channels will not be used, because using an extra channel for just one or two people would be an unnecessary overhead.
If the situation needs it, we will use even some other channels that the ones listed (either more chat channels, or /ooc or /shout or /gu). If that happens, the raid leader will ask the appropriate people to join such a channel and the channel will usually be announced in the raid manager.
Other people than those mentioned in the list can also join the channels if they wish - for example to learn something more on raids - but if someone does, please do not interfere with what is going on in that channel. The people who are using the channel have enough work, and reading unnecessary chat would only make it harder for them.
I already mentioned it, but I can not stress this enough: raids are usually very busy. This is especially true for the raid leader and people to whom the raid leader delegated the important raid jobs (main assist, main tank, healer leader, puller, loot captain, and so on). Please try to keep the communication not related to the raid to a minimum. Use tells as much as possible; if a message is meant for a specific person, there is no reason why 50 more people should need to read it (and then see that it's not for them). On the other hand, if you have a general question about the raid, ask in group chat or in dofraid; don't spam the raid leader with general questions that someone else can answer.
When sending someone a tell, be as specific as possible. Don't say just "yes" or "me", use the whole sentence, because otherwise it's likely that the target of the tell will not understand. Does "me" mean that you want that loot, or that you need a buff?