This is a post that will hopefully help out priests who are new to PvE holy and cannot decide which talents are better than others, since there seem to be so many asking about it. Granted this is not an end-all spec, but 90% of it is the best way to go for the most effective healing/mana regen.
Here's my explanation of my spec(this is for raiding/heroics):
Unbreakable Will: 0/5
- No need for this in PvE
Twin Disciplines: 5/5
- This is a must-have. This will increase healing on almost all your essential spells: Renew, Prayer of Mending, Circle of Healing, and it will also increase the damage your Power Word: Shield absorbs.
Silent Resolve: 0/3
- Assuming your tank doesn't blow monkey balls you will NEVER have a problem with threat, even in 5-mans. Your spells will also not get dispelled so no worries there.
Improved Inner Fire: 3/3
- Pretty self-explanatory, additional spell power is always nice. With 3 points this gives you a total of 54 additional spell power. It's also kinda nice for soloing to have the extra charges so you don't have to re-cast it as much.
Imp. Power Word: Fortitude: 2/2
- You should make sure at least one priest in your raid has this but there's not really any other talents worth taking so you might as well take it for your 5 mans/soloing too.
- This used to be decent back in the day where the effect caused you to suffer no pushback at all. Now it's pretty much worthless in PvE AND PvP.
Improved Power Word: Shield: 0/3
- This is only worth taking if you are speccing deep into discipline where you use all the shield talents. There are many better things to spend your points on as holy. Skip it.
Inner Focus: 1/1
- Pretty much a must-have. Using this does NOT put you into the 5 second rule since your spell is free of cost. So, it is good for that on top of saving the mana from the spell. I usually use this for a greater heal, because if it crits it's a huge heal on the tank, plus an inspiration proc, plus a 50% chance to get a free flash heal from Surge of Light.
- No questions asked. Any priest without this talent regardless of spec is not very bright.
That's all I would take in the Disc tree for speccing holy.
Healing Focus: 0/2
- You have so many instant cast spells and are so rarely taking damage in raids(and usually 5-mans) that this really is not worth taking. It's good for PvP but that's it.
Improved Renew: 3/3
- It's silly to not have this. Renew is an extremely powerful hot and 20% of your healing done should come from this. Anything you can do to make it better you should not skip over.
Holy Specialization: 5/5
- 5% crit is great. Not only do your spell crits proc Inspiration, but they also can proc Surge of Light and Holy Concentration which all contribute to mana preservation. Take it.
Spell Warding: 0/5
- PvP Talent.
Divine Fury: 5/5
- Faster casting Greater Heals is amazing.
Desperate Prayer: 0/1
- More of a PvP spell. Rarely are you the only person dying in a raid or 5-man so it's not that useful.
Blessed Recovery: 0/3
- PvP Talent.
- A great talent, 25% armor is quite a bit when your tank is getting to 25k+ armor. This helps out all of the healers by causing the tank to take less damage.
Holy Reach: 2/2
- Even though CoH is getting nerfed this is still great. You will possibly be using PoH more often now and this also helps that. 20% is quite a bit. If a 4th person is too far away your CoH may only heal 3 targets instead of up to 6(with glyph).
Improved Healing: 3/3
- Saving mana is always good, especially on our most efficient heal.
Searing Light: 0/2
- DPS Talent.
Healing Prayers: 2/2
- Very good. You should constantly be using Prayer of Mending so saving 20% mana on it is great. This will also help you out even more when you start using Prayer of Healing more after the CoH nerf.
Spirit of Redemption: 1/1
- 5% spirit is sexy. Adds to mana regen and spell power if you take the next talent. Plus, sometimes being able to add those heals after you are dead can save the day. Too bad we won't be able to spam free CoH in our form anymore though.
Spiritual Guidance: 5/5
- A must-have talent. This way, you essentially get "free" additional spell power on items with spirit, meaning you aren't paying item points for it.
Surge of Light: 2/2
- Great talent. Not only does this proc give you a free flash heal(or smite if there is no one to heal) but it will not put you in the 5SR.
Spiritual Healing: 5/5
- A must-have holy talent. 10% on all heals is fantastic.
Holy Concentration: 3/3
- Amazing talent. Free Greater Heals are always welcome. And, again, this does not put you into the 5SR.
- I don't want to waste a talent point on this stupid spell. It's up to you. This is VERY situational, and causes people to have to stop dpsing/healing to go find the lightwell and click on it. Not worth it imo.
Blessed Resilience: 0/3
- PvP Talent.
Empowered Healing: 5/5
- No reason to not have this. Pretty self-explanatory.
- Since you can no longer down-rank this is very useful. I like to try to use my greater heals so that they will overheal the tank but only slightly, i.e. 100-500 overheal. This way you get more than the mana worth out of the spell. NOTE: You do not get mana back from spells cast with Inner Focus, Surge of Light, or Holy Concentration.
Improved Holy Concentration: 3/3
- An additional 15% chance of getting a free spell is almost worth it right there, but on top of that the BASE cast time is reduced by 30%, i.e. your flash heal would be reduced to a 1.05 sec cast or your Greater Heal would be reduced to 1.75 sec cast and THEN your spell haste would be factored in, thus essentially giving you 2 flash Greater Heals with one of them being free.
Circle of Healing: 1/1
- Duh. And no, it will not be worthless after the nerf. You just can't sit there and spam it like a baddie. It's still more than worth having, especially with the glyph.
Test of Faith: 0/3
- This is a decent talent, I just decided to put value into others over this. It is not a talent you can rely on, and in most cases your targets will not often be below 50%. It is still good though considering the addtional 6% crit could proc SoL/HC and give you a free heal and/or faster cast rates. If you never have mana problems you might want to consider taking this over Serendipity.
Divine Providence: 5/5
- Duh again. Lots of healing on spells increased here plus turning your PoM into a 7 second cooldown. That means you can cast an additional PoM for every 3 you could normally cast. You might say that your charges never run out in 7 seconds anyway but there are many situations where they do. Patchwerk is a biggie, and any fight where everyone is constantly taking damage(Sapphiron, KT, Malygos, Heigan if they are baddies). With the extra charge from the 2pc T7 bonus it is superb.
Guardian Spirit: 1/1
- This isn't necessarily a must-have, but it's a spell I will always have. It could save your entire raid from a wipe if your tank were about to die - it increases ALL healing received by 40%(and I wonder if anyone can tell me whether or not hots that were already on the target are increased by this) and a 50% total health heal is freakin nice. Not only that, but you can cast it on yourself in screenshots!
Glyph of Circle of Healing - Still excellent even after the nerf. In fact it might be MORE useful after the nerf because you will want to heal as many people as possible whenever that 6 sec cooldown is up.
Glyph of Flash Heal - Pretty much a must-have, especially since you will find yourself using it more after the CoH nerf.
Glyph of Renew - Arguable. You actually end up healing for the same amount but in a shorter time. I like it because it makes it less likely for it to get over healed by paladins and shaman.
Glyph of Spirit of Redemption - It's not best to rely on something increasing the healing you can put out when you're dead, but whatever floats your boat.
Glyph of Prayer of Healing - Decent. A nice additional hot that you don't have to worry about. Unfortunately you can only use this spell on your group so it's more useful in 5 mans.
Glyph of Shadowfiend - This is the only must-have minor glyph for any priest spec. There are many times where your fiend dies prematurely out of your control so it's very nice to have.
The rest of the minor glyphs are all up to you, and none of them are really NEEDED so you can skip them if you want.