Why hit is important
Those of you who already know everything can go ahead and skip this section. Still here? Good...I'm glad I'm not the only one who isn't omniscient.
Here's how hit breaks down:
When you cast a spell at an enemy, you have a percentage chance to hit that enemy with your spell. This chance goes up and down based on two variables--your level relative to the enemy's level, and your hit rating. If your level is equal to your enemy's level, and your hit rating is zero, you have a base chance to hit of 96%. This means that on average, your spells will miss that target one time out of every twenty-five times you cast them. That may not seem like much, but it totally is.
Raid bosses are considered three levels higher than you, which makes them level 83 when you are level 80. Your base chance to hit them is only 83%. That means that almost one in five spells will miss them. Essentially, when you enter a raid instance without a capped hit rating, your DPS is going down by a flat 17%.
At level 80, to you need to pick up 26.232 points of hit rating to gain 1% chance to hit. 446 points of hit rating will get you to a 100% chance to hit, effectively capping you. Until you get to that point, no single statistic will grant you as much of an increase in pure DPS as hit rating, and the comparison isn't even a close one. Every 26.232 points of hit rating you pick up, prior to hitting the cap, gains you a flat 1% damage increase. Point for point, that's absolutely unparalleled.
If you're still on the fence about the relative importance of other stats, consider this: If you are short of a 100% chance to hit, every single other stat suffers directly. If you've been stacking crit, and neglecting hit, and your chance to crit is 40%, but your hit chance is still 83%, you might as well subtract 17% from your crit chance, because you can't crit if you can't hit. Similarly, that 17% can also be subtracted from every other important Mage stat. Your spellpower will be 17% less powerful. Your haste rating will be 17% less...hasty. Your mana pool will be 17% smaller, for all intents and purposes, because you'll be missing 17% of the time, making those spellcasts a complete waste of mana.
Until it is capped, no other stat is as important as hit rating. Though they're becoming more and more rare these days, you'll still run into people who will argue that fact. These people are uninformed, and might also have some sort of cognitive limitation, so be nice to them. They may also believe things like "rainbows are made of skittles," and "Antifreeze tastes great!" If you plan to raid, cap your hit rating first, and worry about the rest of your stats subsequently. This is, quite simply, the most effective way to increase your raid DPS. I'm not sure I can state it any more plainly than that.
How to get it
The first thing every Mage can do to increase their hit rating is to talent into it. Mages have two hit-increasing talents. The first, Precision, is found on the second tier of the Frost tree, and gives a 3% chance to hit for the cost of three talent points. It affects all spells. The second, Arcane Focus, is located on the first tier of the Arcane tree, and also gives 3% hit for three talent points. It only affects Arcane spells. These two talents stack with each other, which means that Arcane Mages have an advantage when capping their hit. They can gain 6% hit through talents, while Fire, Frost, and Frostfire Mages can only get 3%.
There are a few raid buffs and debuffs that can help Mages cap their hit, at least while raiding with the right classes. Draenei come pre-packaged with Heroic Presence, which grants a passive 1% hit chance increase to those grouped within his specific party. Balance Druids can throw a debuff on the boss called Improved Faerie Fire that increases everyone's chance to hit them by 3%. Shadow Priests can keep a debuff called Misery up pretty much constantly, and it also provides an extra 3% chance to hit for the raid. These two debuffs don't stack with each other, so the maximum they can help you is that 3%. The Draenei buff stacks with everything. Depending on your raid makeup, you can use these to provide you with some flexibility in how you gear for the raid.
There are a couple of food items, Worg Tartare and Snapper Extreme, that will buff you for 40 hit rating. If you're under the cap, the hit rating is far better for you than, say, spellpower food.
Aside from those various buffs, you'll have to reach the cap through gear, gems , and enchants.
So how much will you need?
If you're an Arcane Mage with Arcane Focus and Precision, you'll need 289 hit rating. If you have the benefit of Faerie Fire or Misery, you'll need 210 hit rating. If you have a Draenei in the party, in addition to one of those 3% debuffs, you'll only need 184 hit.
If you're a Frost or Frostfire Mage with Precision, you will need 368 hit rating. With either of the two 3% debuffs, you'll need 289 hit rating. If you throw the Draenei buff into the mix, you'll need 263 hit rating.
If you're a straight Fire Mage with the normal Torment the Weak spec or a traditional Fireball spec, you're screwed. Your spec doesn't allow for taking Precision, so you'll need the full 446 hit rating to reach the cap. With either of the debuffs, you'll need 368, and with a Draenei in the party, you'll still need 341. These are powerful specs, but only if you can get your hands on a lot of hit gear.
Where do I get all that gear?
Seriously, that's where it all is. Problem is, if you're in an Ulduar guild and your Mage isn't hit capped, good luck getting a spot in the raid to get some of that sweet sweet gear.
Still, though it isn't as plentiful elsewhere, you can certainly find it prior to getting an Ulduar invite. I'd start with the always popular epic Tailoring double-whammy: the Ebonweave Robe and Gloves. Those are easy to get ahold of (either gather the mats and find a tailor, or snag them at the auction house), and will net you a quick 119 hit rating. You can pick them up immediately upon hitting level 80, and take them proudly into Naxx.
While you're there, you can hopefully pick up a few of the several good hit items found therein. Just to name a couple: Loetheb drops the Sulfur Stave, Grand Widow Faerlina drops The Watchful Eye, and Anub'Rekhan drops the Gloves of Dark Gestures, and they all do so in normal(10-man) mode. Heroic mode yields a bunch of other stuff with hit rating on it.
If you don't feel ready to step into a raid instance yet, you can pick up quite a bit of hit gear from Heroic instances, including the Mark of the War Prisoner from Cynigosa in heroic Violet Hold, and the Girdle of Bane from Ymiron in heroic Utgarde Pinnacle. Even if you can't get what you want to drop, those Emblems of Heroism you'll be picking up can be used to fill in gaps in your gear. An example would be the Ward of the Violet Citadel, a fantastic off-hand item that also oozes with hit rating, and is a steal at only 25 emblems.
You can even pick up a nice weapon from the Argent Tournament in the Blade of the Keening Banshee. Your gearing options are almost too numerous to even bother listing. There are faction rewards, crafted items, world drops, etcetera. It doesn't matter how you get it, just get it.
There are also several gems and enchants that can help you itemize. You can apply Icewalker to boots, Precision to gloves, and Accuracy to weapon. Your gem options include the Rigid Autumn's Glow and Veiled Monarch Topaz, among others.
What about PvP?
I'm glad you asked. You still need hit rating for PvP, just not quite as much. The level difference still applies, but if you're at level 80, your opponent will never be any higher than you, meaning you only need to cap from that default 96% level. With no talents in Precision or Arcane Focus, you'll only need 105 hit rating to cap your hit rating against a player-controlled opponent of equal level. Truthfully, you'll probably get this amount without even trying.
Even if you don't, you really don't need to lose any sleep about it. Having maxed out DPS simply isn't as big a worry in PvP, so if you're a percentage or two away from being capped, it just isn't as big a deal. Nobody likes to miss, so don't avoid hit rating, but there's a reason none of the game's PvP gear comes with the stat. Other stats (stamina, spellpower, resilience, crit, etc.) are prioritized higher for PvP, and that's just the way it is. Still, I know I feel pretty strongly about hit rating when that crucial Polymorph misses at the absolute wrong moment. Pick up a bit of hit. You won't regret it.
Let me reiterate one thing, but add a caveat: Hit is the most important stat in the game for Mages, but only until it is capped. At that specific moment, it becomes utterly worthless. Reach the cap, but once you do, as you pick up more gear with higher hit numbers on it, make sure you do a bit of shuffling to stay right at that cap. Going over it only wastes stat allocation that could be used other places.
For instance, if you're at the cap now, and then you get a drop in Ulduar that takes you 20 points over the cap, you can then replace the Precision enchant on your gloves with a spellpower one. Gear intelligently as you strive for the cap, keeping in mind items that you may be within your reach.
And whatever you do, don't believe the troll who tells you he ran Ulduar just the other day with no hit rating at all, and his DPS was phat. He's lying, and even if he isn't, he's a moron. Or a Warlock. Meh, either way.
Every week Arcane Brilliance teleports you inside the wonderful world of Mages and then hurls a Fireball in your face. Check out our recent three-part guide to professions for Mages, or our look at a few ideas for dual speccing your Mage. Until next week, keep the Mage-train a-rollin'.