This is much later than I’d hoped. I’ve been working on layers of procrastination. I impress myself sometimes.
Due to their incredible versatility, Paladins are one of the most complex classes and there’s a lot to learn about them. As such, I’m going to split my discussion of Paladins into 2 or 3 parts. I may be cruel to Retadins and discuss them with Tankadins.
Healing paladins are great. Can I come out and say that? Well, I did. They aren’t squishy, they’re great at doing their job, and they have the most impressive arsenal of buffs.
Blessings
Paladins have 10-minute “regular” blessings, and 30-minute Greater Blessings. Not all of their blessings have a greater version, but most of the raid blessings do. The greater blessings are cast on all members of the same class in a raid, which means that if your feral tank needs Light and you, the Resto druid, need Salvation you’re probably going to end up with 10-minute buffs.
Light- Increases the effect of Holy Light spells; this is good for whoever is going to be getting a lot of Paladin heals
Salvation- My personal favorite. Decreases threat by 30%. Some DPS classes are prone to whining that they don’t need Salvation and would rather have Might or Wisdom to increase their DPS. You may find it beneficial to point out that the less they pull aggro off the tank, the more DPS they get to do before getting smashed in the face by the big, scary boss.
Might- Increases attack power. This is good for melee attackers and hunters who can watch their aggro.
Kings-Increases all base stats by 10%. It does require your pally to go 10 points into the Protection tree. However, I don’t think I’ve met a Paladin without it. Generally if you have 2 Paladins, the buffs go something like, “everyone gets Kings and also something else.”
Wisdom- Increases mana regeneration (41 mp5 without talents). This is mana per 5, so it isn’t going to help your Innervate at all. Which is not to say that it isn’t nice to have. It’s definitely great, but think about whether you’re running out of mana or topping the aggro list first to help the Pally choose which blessing you should have.
Sacrifice- I’ve only really ever seen this be useful in the Maiden fight in Karazhan, but it’s definitely worth knowing about, especially if your Paladin isn’t aware of it’s utility in Kara. It transfers 105 damage taken by the recipient per hit to the Paladin for thirty seconds. Using Blessing of Sacrifice in the Maiden fight allows the Paladin to be woken up from Repentance so they can get back to healing the tank.
Auras
Paladin Auras are buffs that the Paladin has on that affect all party members within 30 yards. They are free, instant casts which trigger the global cooldown. However, each paladin can only have one aura up at a time.
Devotion- Armor bonus
Retribution- Causes holy damage to any creature that hits a party member
Concentration- Gives a chance (base 35%) to ignore spell casting delays caused by damage
Shadow Resistance- Increases Shadow Resistance
Frost Resistance- Increases Frost Resistance
Fire Resistance- Increases Fire Resistance
Healing & Related Spells
Paladins have 2 main healing spells. These are Holy Light, a huge 2.5 second cast, and Flash of Light, a 1.5 second heal that is significantly smaller than Holy Light, but incredibly mana efficient. Almost all Holy Paladins will also have Holy Shock, which is an instant cast heal for about the same amount as Flash of Light but less mana efficient. Lay on Hands is another little gem that Paladins have. It heals for their entire mana pool, also costing their entire mana pool. An important thing to remember here is that if they use Lay on Hands and ask for an innervate, it probably isn’t going to help them much since most Paladins have very little Spirit on their gear.
Paladins can also dispel poison, disease, and magic debuffs.
References:
The Light and How to Swing it: Bless You

Hunters and rogues should never get Salvation in preference to Kings and Might, and for hunters add Wisdom to that list.
Sacrifice, Justice and Freedom are 30s blessings, and have limited uses, freedom is typically kept for the tank and sacrifice is quite useful in high damage situations on classes, or to break a stun. However none of these should typically be used over the 3-4 main blessings for a class, consider sacrifice to be a potential blessing when sanctuary would be used, but only on the MT, helps keep your mana up as well and will reduce the damage he takes by ~ 100, rather than sanctuaries maybe 80.
Flash of light spam can basically be kept up for the duration of a fight by a holy or protection paladin, its that mana efficient, healing ~1.5k with +2k healing bonus. Holy Light is also a relatively fast cast however cannot be maintained as a spam spell for long periods of time. Holy shock is situational as its range is much shorter than the other 2 spells (20yards vs 40), and so the paladin must be within range (often hard). Lay on hands should not be considered a heal so much as an emergency response, its on a 1hr cooldown and drains you mana, its a “do or wipe” button normally to buy time.