A word of caution
What it is and what it is not
Raid calling is about verbalizing the important cues during a boss fight. But before we get to deep into the technique, let's make sure we establish what it's not. Raid calling isn't necessarily raid leading; a raid caller doesn't necessarily make the calls like "let's use this strategy" or "please use this spec for this fight." Sure, that could be the same person, but I don't mean to imply the role itself commands those duties.
There are definite strategic decisions a raid caller might need to make. For example, when you have a pair of tanks trying to control the golems of Omnotron, the caller might ask "move them to the wall." That's just part of the role.
The basic intent of raid calling is to announce the boss abilities to which the raid group, or large portions of the raid group, must react. For example, when Toxitron uses Poison Protocol, having someone announce that slimes are on the floor helps make sure the entire raid is on notice. When someone is hit by Blackout, you want everyone to collapse on that player.
When you're making calls for a raid, you can't just announce the name of the ability. Especially after six years, a lot of abilities have similar names. Heck, the names can be confusing on their own right. Just shouting "Dazzling Destruction!" isn't necessarily meaningful. It needs a little bit of context.
When you call, try saying things like, "Blackout -- collapse on tail." You are saying a few extra words and might need to say them quickly. In general, say the name of the ability and a short bit of instruction. Some good examples are:
Not everything is viable to being raid called. For example, you're not going to be successful calling things like interrupts. Even the long version of Shadow Nova
goes by too fast for that. The only way to call something like that is to say, "Focus on interrupts."
You should also be careful not to step on raid members. Your healer corps, for example, probably has a decent idea of what they're doing. I've known more than one healer to get very, very tired of hearing "Big heals!" Healers can generally tell big heals are needed by the precipitous drop in the tank's health. At the same time, it can be helpful to get some verbal warning that those heals are about to be needed.
You'll have to work together to figure out good calls and bad calls; this is why raid groups get together, get to know each other, and expand together over time.
A lot of abilities make certain areas of the floor dangerous, which means you want people to move out of them into a specific place. Since I've used Deep Breath as an example before, let's take another look at it. When you're fighting a Deep Breath dragon, it puts a patch of fire on the ground. It's a long line of fire, and you need to call to raid members to make sure they don't stand in it.
Directions like "left and right" are about useless. If your camera is turned, you have a different "left" from everyone else. Try to use specific cardinal directions as they appear on your minimap. "Abandon north" is more effective than "dance left."
I almost feel silly for saying this, but the raid caller should try and work with his raid to learn the best way to make calls. It's a feel-good thing for the raid, sure. More importantly, though, you need to work with other raid members to "speak their language."
Trying to make sure you're using the best jargon for everyone involved will make your calls more comprehensible. Some raids never use the actual boss ability names; instead, they use a general kind of language that everyone understands. In my guild, for example, every patch of fire that we shouldn't stand is called a "void zone." It doesn't matter if the "void zone" is fire, ice, or rabid wombats; we call it a "void zone." It's inaccurate, sure, and I can see how calling a pit of fire by the name "void zone" could bother some people. But to us, "void zone" is just code language for "don't stand in that." It's fast, easy, and we all know exactly what it means.
The trick to raid calling is fast, easy communication. As with all communication, tailor your language to your group.
Ready Check shares all the strategies and inside information you need to take your raiding to the next level. Be sure to look up our strategy guides to Cataclysm's 5-man instances, and for more healer-centric advice, visit Raid Rx.