Rotation, Cooldowns, and Abilities
On this page, we list your Discipline Priest core abilities and how they should be used together (rotation) in World of Warcraft WoD 6.2.2. We also explain when to use your various cooldowns. Then, we go deeper and present all the subtleties that you will need to know if you want to excel at playing a Discipline Priest.
1. Rotation↑top
Healing is in great part based on your ability to react to the damage that the raid takes, and as such there is no set rotation. Rather, you must understand what spells are best suited to the different situations that can occur during a raid encounter.
Below, you will find the optimal use of your abilities, and it will be up to you to then combine them efficiently in combat.
1.1. Single Target Healing
To begin with, you should use 
Penance on cooldown on the tank, or on another target that is taking damage.
Then, you should make ample use of 
Power Word: Shield. This will not only prevent damage, but also increase your haste thanks to 
Borrowed Time.
Normally, you will be using 
Words of Mending as your tier 7 talent, which means that 
Prayer of Mending will be cast passively. You should only refresh it manually if it is expiring.
If the target is taking more intense damage, then you can use 
Heal and 
Flash Heal (in more urgent situations) on them, but as a Discipline Priest you are not well suited for this task, and you should instead rely on other healers in your raid for this type of healing. In the event that you want to focus on single-target healing, you should be using the 
Clarity of Will tier 7 talent instead of Words of Mending.
1.2. AoE Healing
AoE damage should normally still be healed in roughly the same way as we described above. Your main tool is Power Word: Shield.
Prayer of Healing should only be used under certain conditions. You should use it if you have the 
Archangel or Empowered Archangel buffs active, or if you have your 
Power Infusion buff up. In any case, when using Prayer of Healing, you have to make sure it will do very little or no overhealing, as otherwise Power Word: Shield becomes a better alternative.
If you are using Words of Mending as your Tier 7 talent, Prayer of Mending will be applied passively and, as above, if it is about to expire, then you should re-cast it manually.
1.3. Evangelism, Atonement, and Dealing Damage
Atonement healing is quite inconsequential. In the presence of other healing options, casting spells affected by Atonement will always result in an overall healing loss. However, stacking the 
Evangelism buff so that you can use Archangel is beneficial.
The ideal way of stacking Evangelism is to cast 
Power Word: Solace on cooldown (which will generate 3 out of the 5 stacks required during the 30-second cooldown of Archangel) and to obtain the remaining 2 stacks by using either 
Smite (if you have to heal raid members with Penance) or Penance (if you can afford to use it offensively).
2. Cooldown Usage↑top
Pain Suppression should be used on a tank, before a damage spike. Alternatively, it can be used on a raid member who is targeted by a very damaging ability.
Power Word: Barrier should be used to mitigate intense AoE damage; it requires the raid to be stacked in one place.
We expand more on the cooldowns that you gain from your talents in a subsequent section.
3. Optional Read: Mastering Your Discipline Priest↑top
While the guidelines we have given so far will enable you to perform very decently as a Discipline Priest, there are many subtleties which you need to be aware of, if you want to play your character to its full potential.
3.1. Important Mechanics
In order to use your spells appropriately for the situations you encounter, you must first understand several aspects of the Discipline specialisation.
3.1.1. Mastery and Absorption Effects
The Discipline Mastery is Mastery: Shield Discipline. Essentially, your Mastery increases the amount of healing your spells do, as well as increasing the damage absorbed by your absorption effects.
Discipline Priests have two absorption effects:
Power Word: Shield is quite simple. You place a shield on a target, which absorbs a certain amount of damage (affected not only by your Mastery, but also by your spell power). Applying a shield to a target causes the 
Weakened Soul debuff, which prevents them from being shielded again (by you or any other priest) for 12 seconds. Power Word: Shields benefit from your critical strike chance, absorbing twice as much damage when this effect procs.
Your 
Divine Aegis passive ability provides you with a passive absorption mechanic. Each time you critically heal with a spell (including multistrikes), a shield is placed on the target that absorbs damage equal to 100% of the amount healed. This absorb is added to the heal amount, but the heal is not a critical effect, rather just the default amount. In other words, instead of a critical heal being a 200% heal, thanks to Divine Aegis, it is a 100% heal and a 100% absorption effect.
Divine Aegis has a 15 second duration, and each new application of the buff will stack on top of the previous Divine Aegis (merging the remaining amount of absorption with the amount of absorption created by the new shield) and refresh its duration. Note that the amount absorbed by Divine Aegis is limited to 60% of the casting Priest's maximum health.
Power Word: Shield and Divine Aegis can co-exist on the same target at the same time, without any kind of interaction between them.
Absorption is a key element of Discipline healing. Shielding people is a means of preventive healing, which reduces the spikes in damage taken and ensures that damage is more predictable.
3.1.2. Borrowed Time
After each cast of Power Word: Shield you gain the Borrowed Time buff. This causes you to gain an additional 40% haste from all sources for 6 seconds.
You will essentially always have this buff from the way you normally shield players.
3.1.3. Enhanced Leap of Faith
Enhanced Leap of Faith causes your first non-period heal cast on a target on which you have used Leap of Faith (within a 10-second window) to heal for 50% more. Given that Leap of Faith is not on the global cooldown, it is quite easy to use a technique of casting Leap of Faith on someone just prior to healing them.
3.2. More on Cooldowns
3.2.1. Tier 3 Talents
Power Word: Solace should be used on cooldown, as it will restore Mana and help generate Evangelism stacks.
If you have chosen 
Surge of Light, then simply be prepared to use your procs, so that they do not overwrite each other.
Mindbender should be used on cooldown, provided that the Mana it grants you will not go to waste.
3.2.2. Tier 5 Talents
Power Infusion should be used whenever a period of intense healing is coming up, or simply when you want to conserve your Mana. Exceptionally, you can use it to deal more damage, if the encounter calls for it.
Spirit Shell should be used whenever there is high sustained damage to heal. You should aim to use it as many times as possible throughout the fight. It can also be used to pre-shield a target before they receive a lot of damage.
You will obtain the benefits of 
Twist of Fate passively, so there is nothing for you to do about this talent except enjoy the increased healing.
3.2.3. Tier 6 Talents
For the majority of situations, you will prefer 
Halo. For it to be effective, you need to be 25 yards away from the targets you wish to heal. Note also that the Mana cost of Halo is very high.
The other two talents in this tier are not worth using, as Power Word: Shield is actually a superior choice.
3.2.4. Tier 7 Talents
Clarity of Will is basically a strong Power Word: Shield that does not have the drawback of applying the Weakened Soul debuff, but which is considerably more expensive, and also has a casting time. You should use it much in the same way that you already use Power Word: Shield to prevent damage, by applying it on the tank or other single target you are healing.
Words of Mending is entirely passive, so you do not need to worry about it.
Saving Grace is not a good option, and should never be taken in its current state.
Content gathered and originally posted by Vlad at http://www.icy-veins.com/wow