Through a combination of pugging, guild runs, and quasi-guild runs, I've managed to do all the heroics in Cataclysm. They're really good, and moderately hard. They really reward knowing the fight and executing correctly. Here are some tips that may help Holy paladins working on instances.
- Cleanse - Seriously, Cleanse early, Cleanse often. Cleanse is expensive, so you do have to watch for debuffs that stack faster than you can Cleanse. If you're doing heroics exclusively, I'd strongly suggest Glyph of Cleanse.
- Run First, Heal After - If you are ever presented with the choice of running to avoid a fight mechanic, or finishing your cast, choose to run. Fight mechanics are far more likely to kill people than straight up damage. As well, practice healing while moving with Holy Shock and Word of Glory.
- Use Cooldowns - Get into the habit of using your cooldowns religiously. We have 5 cooldowns, in addition to any trinkets: Lay On Hands, Blessing of Sacrifice, Divine Favor, Avenging Wrath, and Guardian of Ancient Kings.
Hand of Sacrifice is pretty strong now. You get a lot of self-healing with Protector of the Innocent, so it usually does not hurt to use it on the tank liberally. I like using it at the start of trash pulls when it's up.
Use the shorter cooldowns on trash. They'll come back up in time for the bosses. I generally like alternating Divine Favor and Avenging Wrath on trash pulls. Use cooldowns at the start of the pull, when you have the most mobs beating on the tank.
Lay on Hands is very powerful. It essentially resets a tank's health to full, and gives you a chunk of mana with the Glyph. Use it aggressively on boss fights, especially when it feels like you've fallen behind.
Guardian of the Ancient Kings casts the same single-target spell on the same target that you do. Ideally, you want to use Divine Light to maximize the healing done when your Guardian is up. I like popping GoAK at about 20%-ish, to stabilize the fight and bring it home. But use it aggressively and early if you need to.
I also don't like overlapping cooldowns. Unlike DPS, it feels like you get more time with stronger heals if you spread them out.
Use cooldowns aggressively, and don't be afraid to "waste" them.
- Resistance Aura - My aura of choice is Resistance Aura. Things just seem more stable when Resistance Aura is up. As well, you can use Aura Mastery as an extra cooldown during periods of mass damage. I do switch to Devotion Aura if there is no Fire, Shadow or Frost damage in the fight, but that's pretty rare. Raid damage tends to be magical.
- Judge Often - try and judge as often as you can, especially on adds. It's extra damage and helps keep your mana high.
- Use Holy Radiance to Move Faster - The talent Speed of Light increases your run speed when you cast Holy Radiance. A lot of times, the entire group will need to move because they are taking damage. If you pop Holy Radiance as you start moving, not only will you heal people as they take damage, but you will move out of the fire that much faster.
Those are some tips for paladin healing in heroics. The biggest thing though, is familiarity with the fights. Once you know what to do, they become a lot easier.
Any other tips for Holy Paladins?