If you're a raiding Priest or you don't see yourself engaging in a whole lot of PvP, then odds are good that you won't have any of these talents. But if you do plan on supporting your friends while they go mopping up some Horde/Alliance, then you may want to consider the following:
Martyrdom: This 2nd tier talent allows you to avoid spell pushback after being hit by a critical strike. At the same time, you can increase your chances of resisting any interrupts. It's reassuring to know that after being hit really hard you can come back with a heal on yourself.
Mana Burn: While it may be rare, you may see an opportunity in combat where you don't have to heal anyone. Keep the global cooldown going and start casting Mana Burn on targets of opportunity. Go after their healers. No one can heal without mana. Deprive them of their resource and they will not be able to support the other players around them. I would rate this as a must have talent.
Focused Power: This reduces your Mass Dispel to a 0.5 second cast. This spell is huge against those pesky Paladins and Mages who use their invulnerability spells.
Focused Will: This stackable buff activates after being critically hit. It reduces your damage taken and increases the healing done on yourself.
Power Infusion: Again, this is another staple talent in the PvP Priest arsenal. It's going to largely depend on the other classes around you. But a Mage with Power Infusion, Icy Veins, Heroism or Bloodlust at their disposal is truly a force to be reckoned with.
Pain Suppression: Used well, it can save the life of yourself or your teammates in key situations.
Blessed Recovery: This is another staple talent you'll want to help get some of the health back you lost from Joe Shaman who has done nothing but Lightning Bolt you. Repeatedly.
Spell Warding: You're going to get blasted by spellcasters often. Maxing out Spell Warding helps to reduce that damage by 10%. I guess you could say that this helps you live 10% longer (until that Mortal Strike Warrior comes barreling in).
Blessed Resilience: While it's highly unlikely you'll go this far into the Holy tree if you intend to engage in any kind of PvP, it's a consideration for deep Holy Priests who want to play around with the spec for a while and retain some viability in both PvP and raiding. (Thanks to commenter Anid Maro)
I'll cover some entry level gear that you can obtain for yourself and what gems and enchants to augment them with in this section.
The set we're looking for is called the Mooncloth set. You can pick the items up from various reputation vendors around Outland. It's a good beginner set to have when you start PvPing. The entire set will cost a little under 70G.
All of the other items can be obtained via honor. These include:
When it comes to gemming, try to aim for both Stamina and Resilience as often as possible. Remember as a Priest, you're effectively running around with a pink, neon gank me now sign. Try to aim for a little over 10000 health and 400 resilience before swapping out your gems for others. You do not have to follow the gem bonus guidelines, especially if they don't add to your stamina and resilience totals Worry about your survivability first.
A dead Priest is a useless Priest. Never forget that important rule.
Teardrop Living Ruby
Solid Star of Elune
Powerful Earthstorm Diamond
Insightful Earthstorm Diamond
There's been some discussion and debate about which meta gem to use. Personally, I prefer the survivability so I opted for the Powerful Earthstorm. On the other hand, mana is good to have especially in endurance games in arena, so be sure you take that into consideration. Always remember that meta gems must be activated -- one or the other may have a more favorable combination of gems for your gear. Pick the meta that will be easiest to activate so that you won't have to shuffle it around as much.
Glyph of the Gladiator – Shattered Sun Offensive, Revered
Glyph of Renewal – +35 Healing, 7 mp5
The shoulder enchant you choose will largely depend on which Shattrath faction you're aligned with.
Greater Inscription of Faith - Aldor
Greater Inscription of the Oracle - Scryers
Enchant Cloak – Spell Penetration
Enchant Chest – Major Resilience
Enchant Chest – Exceptional Health (If you can't find a Resilience enchanter)
Enchant Bracer – Fortitude
Enchant Bracer – Superior Healing
Enchant Gloves – Major Healing
Enchant Boots – Boar's Speed
Enchant Boots - Fortitude
Enchant Weapon – Major Healing
Hopefully this list will help set you up in such a way that you can help your guildies or team mates dominate the opposition (or at least survive longer than 10 seconds). Come back next week and I'll cover the spells you should be using, when to use them, and basic things you can do against other classes.
Want to find more great tips for carrying out your Priestly duties? Spiritual Guidance has you covered -- before the long hiatus, we looked at threat and examining what kind of healer you were. And don't forget to check the WoW Insider Directory for more priestly info -- there's lots of guides, writeups and discussions over there as well.