Way back in the day, before any of us had the opportunity to actually play the game, Blizzard was in the process of developing the classes of WoW. Rogues were designed to be sneaky stabbers and priests were based around doing heal-y things. Shamans and paladins were created to be in direct opposition to each other. The designated shaman archetype was the offensive hybrid, giving their friends extra damage potential and eventually Bloodlust.
Paladins were the antonym, created to help defend their raid and party from damage and to provide useful buffs. While much of the original intentions have been diluted via homogenization, paladins are still the ultimate defensive class. Unfortunately, in order to perform our role in the face of constantly changing opponents and venues, our toolbox of abilities has become fairly large. We've got a utility spell for nearly every situation, and there are a vast number of situations out there. The key to being an effective paladin is to do your homework and to come prepared.
Get your buffs right
While Cataclysm is halving our Blessing count from four to two, making it incredibly simple to make sure everything is covered, we currently have quite a few different options when it comes to buffing the raid. Blessing of Might only helps physical classes while Blessing of Wisdom is only effective for classes with a mana bar. Blessing of Kings is good for everyone, and Blessing of Sanctuary is really only needed for paladin tanks and groups without a discipline priest around. With so many specific cases for each class, it can be hard to figure out what to buff. If you have enough paladins in the raid to buff all four blessings, then simply coordinate via chat or PallyPower to get all four buffs on the entire raid.
If you're short paladins, you have some decisions to make. Wisdom and Sanctuary are the weakest of the blessings, so drop these two first. Another option is to carry around the Drums of Forgotten Kings, which is a really cheap way to bless the raid with Kings. I carry the Drums with me on my paladin, so I can bless Might or Wisdom on each class, and then use the Drums to effectively get two buffs on everyone. I'll also typically leave Wisdom off of myself if I'm paired with only a paladin tank. It's better for him to have Might or Kings for threat and avoidance than it is for me to have Wisdom, considering my already potent mana regeneration. Finally, Glyph of Blessing of Wisdom can help you keep a 30-minute version of Wisdom on yourself, which is nice if you're forced to buff the other paladins with Might.
Pick the aura for the job
I can't tell you how many times I've forgotten to switch my aura when moving between boss fights. I get distracted by coordinating loot or fighting trash or explaining a fight, and by the time we're already engaged, it's completely out of my mind. Make it a point to check your aura before answering "yes" to a ready check, and you shouldn't get caught with the wrong aura active. You should know which aura you're going to be running before a fight starts, based on the specifics of an encounter.
If you have Improved Concentration Aura, you're pretty much designated to running that aura for the encounter. The same goes for Improved Devotion Aura, though realize that many protection paladins will have this talent as well. Otherwise, you should be choosing your aura based on which will be the most effective when paired with Aura Mastery. On the Lich King encounter, you'll see many paladins actually running Shadow Resistance Aura even though their raid already has Shadow Protection from a priest. The reason is that SR Aura, when mixed with Aura Mastery, can help negate an Infest pulse if there are healers incapacitated. Similarly, you can use Aura Mastery and Fire Resistance Aura to help your raid survive one of Prince Taldaram's Empowered Flames.
Coordinate with your kin
There aren't many abilities in the game that don't stack at all, as otherwise we'd hear tons of complaints from Rejuvenation-spamming resto druids. One of the few spells that actually doesn't stack is Sacred Shield, and that's for a fairly good reason. Blizzard doesn't want to make it possible for there to be so many absorption effects on one target that they're able to bypass an important mechanic. That's also a reason why Weakened Soul exists. While many fights in Icecrown Citadel feature at least two tanks, there are a few where that's not the case. Professor Putricide comes to mind, as one tank is driving the abomination for most of the encounter.
Make sure you coordinate with your fellow holy paladins to make sure that you're putting your shield on separate targets. You can still proc your Infusion of Light HoT when you use Flash of Light on their Sacred Shield target, so there's no real loss. If you each have a designated SS target, you'll ensure that you're not overwriting each other's buff. You should do the same with Beacon of Light and tank assignments as well, ensuring that every tank has a Beacon on them when possible. Finally, make sure that you're covering all of your bases for Judgements. Judgement of Light is massively powerful on certain fights, so talk with the other paladins to make sure it's active.
Prepare your arsenal
Every guild has one. You know who I'm talking about. The one guy who can't seem to figure out how to download Omen and purposefully refuses to put any points into threat reduction talents. The one guy who knows that tank threat is in a precarious position during Lady Deathwhisper's transition between phases, and chooses that time to unload his cooldowns. You know he's going to pull aggro, and you have a choice to make.
You could Hand of Salvation him to drop his threat, but you'll probably need it for some other DPS as Touch of Insignificance stacks up on your tank. You could just let them die, which is probably what they deserve, but Lord Marrowgar didn't go well and you'd rather not have another death on your scorecard. Hand of Sacrifice is an option, but why not just negate the damage altogether? You decide on giving them a Hand of Protection to save them from a few blows.
Knowing a fight's mechanics ahead of time will allow you to coordinate all of your various abilities to be active at the most opportune times. If you know when a big blast of shadow damage is incoming (e.g. Infest), you can have your Aura Mastery finger ready. If you know when your tank will be slowed (e.g. Sindragosa's Frost Breath), you can have mouse already over the tank to cast Hand of Freedom. Knowing which spells you'll be using ahead of time will reduce the reaction time necessary when the moment of opportunity comes. The more you prepare, the better you'll perform when it's your time to shine.
The Light and How to Swing It (Holy Edition) helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Holy 101. We can help you keep a tank alive, heal a raid when necessary and beat the global cooldown. Tanking is a job, DPS is a craft -- but healing is truly an art.