I was chatting with a fellow priest from guild the other day about priestly healing in WoD and given the state of affairs on beta right now he decided he better learn to play holy. Now honestly I'd say its a bit early to get all hysterical but...given the changes coming and the lack of legendary life vests that we won't have to lean on it may very well be worth having a good understanding of Holy going forward.
As always however I do recommend heading into the Proving Grounds and going for the hardest level you have available to get a real idea of what healing without all the bad-aids is like.
As for me, now that our raid team has wrapped up its pilgrimage into SoO I will be focusing on getting my Proven Healer title along with trying to find some dedicated souls to head into CMs with. I don't really care for the priest CM outfit but I really enjoy the CM environment and would like to push that as far as I can if I can find four other no-lifers to join me.
In the mean time here are some helpful hints for Holy from the worst priest in the game. YMMV.
Disc and Holy are very different styles of healing. Disc has a very DPS feel to it in that you have a fairly rigid rotation and are constantly casting. Holy on the other hand is a reactive style of healing and assuming low damage can have significant periods of downtime where casting isn't particularly required, save maybe rolling renew on targets just to keep them topped off.
I recently leveled to 60 as Holy and have since run a few (3 to be precise) heroic dungeons as Holy and I have to say that it just wasn't super intense like healing as disc was. Most of this is due to overgearing from tanks and DPS and shear amount of self healing they can produce. Healing a highly geared blood DK (hey Wort o/) in heroic dungeons required little effort at all.
But let us go in assuming we are healing a poorly geared group and that you need to get the most of your mana.
First up we need to distinguish between efficient cooldown bearing heals and non-cooldown bearing filler spells.
For Holy our CD bearing spells are:
Circle of Healing (CoH) - a relatively powerful AOE heal. In yellow stance the CD is longer than in blue stance. This is also one of our strongest heals while in red stance.
Prayer of Mending (PoM) - PoM is a smart heal that should be applied when off its 10s CD AND not currently sitting on a player likely to take a hit. There are addons to track where it is at and your raid frames should show this as well. I also use a weak aura to track duration, current target, and charges remaining but even the WA is a bit fickle.
Power Word: Shield - unlike disc we have a short CD on PW:S that stops us from spamming it all over the raid. The spell also lacks efficiency when we cast it but it is good in emergencies to allow us a short amount of time to ramp up a strong heal.
Lightspring - LS should be dropped when off CD and you aren't planning to move in the near future, in otherwords on boss fights. This thing is smart and handy and will grant you some breathing room when the fit is hitting the shan.
Guardian Angle (or Spirit, I forget) - one of our long CD OSB used to save a player who is in danger of dying soon. While predominately a tank saver I actually prefer to use it on DPS players, especially clothies, who can't stay out of danger.
L90 Talents - Cascade will refresh renews while in yellow stance and is very strong. That said Divine Star and Halo are damn powerful spells.
Finally in yellow stance you have you have your chakra spell Holy Word: Sanctuary I think. This is a single target heal that does a large amount of healing for cheap. HW:Serenity in blue stance is placed AOE heal for people standing in it.
I mainly stay in yellow stance and only switch to blue for heavy AOE periods. HW:Ser is not super strong and so I see yellow as a more powerful and controlled stance.
While in yellow stance you will want to start renew rolling on anyone who takes damage or has aggro. Follow this up with HW:San targeted heals and since you've taken FDCL as your talent hit them with the free flash heals you proc while renew spamming. Two FDCLs or two Binding Heals or any combination there in will give you access to a cheap and fast Greater Heal or Prayer of Healing. Use GH on single targets or PoH if there are multiple people hurting. If you don't have Serenity at two stacks then use your CoH CD to heal group damage.
Level 90 talent is also a strong AOE heal so don't forget it.
If you do go into heavy AOE damage go for PoM and use binding heal when you have damage. Use FDCL procs to get Serenity up to two stack (so you need to start tracking Serenity) then use PoH if CoH is on CD and L90 is on CD.
You can buff up a cast with synapse springs, or on use trinkets, or things like that if you need it to hit really hard.
Use your Legendary Meta Gem procs (you are tracking those right?) to spam renew or cast your L90 talent.
As far as gear goes, Haste is good for extra ticks on renew and to get cast times down on filler spells. I shoot for a cast time of around 1.2s for spells that start off near the GCD of 1.5s which is nice all around. After that Mastery will convert a % of your healing into a rolling HoT which is nice. Spirit should be comfortable around 10kish with Dysmorph and 12.5k otherwise but you should learn to be efficient with less anyway. Crit is a backgroud stat for Holy in MoP but may gain importance in WoD depending on what things end up looking like.
As always ask questions, do research, and keep exploring and growing. Now go and heal your butt off O/