I’ve put together this little down-and-dirty guide to discipline priest healing because being a Disc Priest these days is, truly, complicated.
The main source of this complexity lies in the fact that Disc Priests are now essentially two distinct specs: the SmiteSpec and the ShieldSpec.
The variance in style of the two versions of disc priesting is pretty pronounced, so disc priests tend to lean quite heavily toward their favorite version of discipline. It’s created something of a rift in the Disc community. Much shouting and pulling of beards.
ShieldSpec focuses on shielding, doling out standard priest healing spells, and managing a variety of cooldowns (Inner Focus, Power Infusion, Rapture) to return mana. It functions similarly to how Discipline worked throughout Wrath of the Lich King.
Pros: Similar to the Wrath disc healing style and thus familiar to Wrath Discos. Intuitive.
Cons: (Possible) lower mana return. Boring.
SmiteSpec is based on an entirely new healing mechanic for Warcraft. SmiteSpec disc priests use a combination of offensive, DPS (primarily Smite) spells for mana return and indirect healing spells, coupled with more classic Discipline direct healing spells (including Shield).
Pros: New and different way to heal, unique to Discos. (Possible) higher mana return. Wings (WANGS!).
Cons: Focus diverted between DPS targets and healing targets. Minimal DPS damage. Unfamiliar mechanism.
Personally, I’ve been running the two specs simultaneously to see which better fits my needs/playstyle, and I have to confess that I lean more towards the ShieldSpec. However, both are viable and fun Discipline Priest options.
Sample ShieldSpec Build
View Liala’s Current ShieldSpec Build

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Sample ShieldSpec Rotation
With this build, I like to Shadow Protection/Fortitude everyone pre-fight. The low-cost instants of Inner Will are worth more to me right now than Spellpower (plus I think the increased movement speed helps me stay out of AoE trouble).
For a rotation I generally bubble (Power Word: Shield) the tank, hit him with Prayer of Mending, then watch. If another DPS is taking a lot of damage, I’ll throw another bubble and a Renew on him or her, and then go back to refreshing Prayer of Mending and bubble on the tank. For a big, quick tank heal I use Penance; for a slow, big tank heal I use Greater Heal.
If damage is going all over the place, I use Inner Focus and then Prayer of Healing; if damage is focused on the tank, I use Inner Focus and then Greater Heal. I use Inner Focus on every cooldown religiously.
Sample SmiteSpec Build
View Liala’s Current SmiteSpec Build

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Sample SmiteSpec Rotation
[Incoming!]