Ok guys, I can help,
First off, WELCOME BACK FSR HEALING. FSR is the five second rule of healing using mana regeneration as your primary source of mana return. After you cast an instant or finish casting a cast time spell a clock will start during which you receive your combat version of your mana regen. After 5 seconds you receive your out of combat mana regen which is substantially better. What this means is that your healing as a priest should always be in bursts and clusters. You need to caste a number of spells together one after the other then stop casting and wait for as long as you can so you can stay outside of your FSR.
Gear wise, you need to re-forge everything you can into spirit. All enchants need to be spirit. All gems need to be spirit or crit or haste, in that order. You need to do the dungeons which contain the trinkets that proc spirit. There are a couple which proc over 1300 spirit in reg dungeons.
You need to flask and food spirit. This is important, you HAVE to learn how to use Potions of concentration. They return 22000 mana over 10 seconds and if you are an alchemist with the new alch stone they return more twords 30,000 mana. These are key. Use them.
Before item score 245 you want to be disc, not holy. This is why. Holy is wonderful love it to death, however it lacks a very important mechanic which disc contains... Train of thought. This ability will be the key to being able to heal as a priest without being oom all the time. Train of thought allows you to decrease the cd on inner focus by about 25% per greater heal cast. The next is Borrowed time. Caste a shield or two for haste then greater heal to effect Train of thought. Always try to use your inner focus for Prayer or healing for group heals. Make sure you are glyphed for the extra hots at the end.
Always try to avoid casting renew and flash heal. These are VERY not mana efficient. Use renew on the tank but thats it. Try to manage dps with heal and your Train of thought cycle ie Prayer of healing, or a shield.
Keep in mind flash heal and Binding heal cost the same and have the same cast time however flash heal heals a bit more but only to one target. If you are hurt and need healing ALWAYS try to use heal or Binding heal. BH works with inner focus too

Don't forget FSR healing.
Ok, Pain supresion and Power word barrier: these are NOT oh shit buttons for the most part. They can be used that way but its very risky. Use these spells when you know that your tank is about to take ALOT of damage. If you use these spells preemptively they will work for you much better. You can also stack them for extra damage mitigation.
The best oh shit button you have is flash heal. If you can slip a shield or renew or pain suppression in there do so but, spamming flash heal saves tanks lives. Its its not efficient but you will just have to recover. Glyph for power word barrier so you get the extra healing.
NEVER use inner fire for boss fights. Always the other one (cant remember the name) the one that give 15% reduction of instant cast spells.
Pick up surge of light and inspiration. Now you Heal reduces the weakened soul effect and can give you a free flash heal thats instant, increses your grace stacks.
I agree, power infusion for yourself. Remember it doesn't work with other haste spells cast on target. If dps is really key dont be completely afraid to put it on the top dps caster.
Front load you shields. Before the tank goes in shield everyone and POM then tank then sit down and drink. You should be able to have shields up and pom on tank and be at full mana by the time the pull happens.
Dont spec into the evangelism/archangel stuff.
Always say when you are going oom, and dont be afraid to ask druids for innervates.
Most important :::::: FSR HEALING-----TRAIN OF THOUGHT/INNER FOCUS cycle.
Please give me feedback guys
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