I rolled a priest. Now what?

So, you want to heal. You rolled a priest, the quintessential healing class. The next question is, now what?

Well, the obvious answer is "level"! Yes, you can level as Holy or Disc if you don't want to buy dual spec, with slight spec variations (most importantly three points in Spirit Tap over in Shadow so you can just stack spirit like a madman as you level and rarely go OOM, even if you kill slowly). It's not as fast as Shadow by any means, but it isn't necessarily the ordeal it is claimed to be.

Here is an example of a Holy leveling spec, with the core of leveling talents at around level 40. You'll heal better than a shadow priest (not that this is necessarily a clutch thing at low levels), and you'll have a decent time killing if you keep your gear stacked in spirit.

I'm honestly not sure how to level as Disc, but here is a spec for the level 40 range. You'll do less damage than a Holy priest, but you'll have a lot more staying power in terms of mana regen and usage. I'd honestly not do this until level 60 when you can pick up Penance and instance grind over questing unless you want to spend a lot of points in Holy (Holy Specialization, Healing Focus, Divine Fury, and Searing Light are all very nice for soloing).

To keep this as painless as possible do two things: keep your spirit high and your wand updated. A basic rotation should involve PW:S on yourself, even as Holy, Shadow Word: Pain, Holy Fire, then Smite once or twice (or more if you really want it dead). Ideally, you want to wand the enemy to death to get as much out of Spirit Tap as possible and to conserve some mana. Survival will occasionally depend on Psychic Scream and healing yourself if you pull multiples.

Once you hit Outland, you can quest, but with the way mob and gear scaling work, this kinda sucks. I'd suggest staying in instances as much as possible or finding someone else to quest with. This also applies to Northrend. The other reason to instance grind is that you will get experience actually healing. Your groups and tanks may suck, but I promise it builds experience and character, and you get shiny blues out of it.

Of course, all this advice is moot if you bought dual spec and quest as Shadow. My only word of caution about dual spec while leveling is that your spell ranks will not automatically update properly 100% of the time, so always double check and make sure your healing and damage spells are of the most current rank if you run into problems.

Now, before you do all of this, it might be best to decide on a spec. Priests have the unique advantage of having two, count 'em, two healing specs to choose from. Both are viable in PvE content, but have different foci.

HOLY
Holy is the quintessential spec for the quintessential healer. It used to be the ONLY viable PvE healing spec, able to both tank and raid heal with ease. Early in Wrath, the tree was redesigned and molded more into an AoE healer, a very powerful one at that. Holy can still single target heal, but to be honest, they are garbage at it with low HPS and mana efficiency problems (i.e. low single target healing numbers and low sustainability).

HOWEVER, while Holy is garbage at tank healing, it can still heal a five man well enough. Holy's shtick is a massive amount of AoE burst, higher heal values than Disc for most spells, an amazing CD as a 51 point, and a button for everything. If you like a lot of heal variance and heal choice, Holy is a good spec for you. If you wish to go into raiding, make sure that raid healing is what you want to do, as it is what a Holy Priest should be assigned to do in a raid.

DISCIPLINE
Disc is a new spec in terms of PvE viability. Its main goal is to prevent damage through damage shields, and provide good single target throughput (when the shields are accounted for). The spec has strong single target burst potential and is highly mana efficient unlike the mana sink that is Holy. While Disc is mostly a single target healing spec, it does have good AoE heals in a five man with Prayer of Mending, Power Word: Shield, and Holy Nova. Disc is a reactive spec that has been described as "paladin-like" in nature. In raids they are often assigned to heal tanks, or prevent/stabilize AoE damage by using Power Word: Shield on the entire raid. Even though Holy is my main raiding spec, I prefer Disc in a five man environment for the mana efficiency and damage prevention potential.

And yes, you can shield a rage tank without hurting their rage gain. If you get yelled at, they haven't read patch notes. The only time shielding a tank may be problematic is in terms of an overgeared paladin tank that is bad at managing Divine Plea uptime. My one word of warning for potential Disc priests is that Disc does NOT show up on a basic meter. While it's nice to be the poster child for why healing meters need to be taken with a grain of salt, a lot of Disc healing is often "invisible" which without a specific Recount plug-in or a World of Logs report, makes it hard to judge your performance on occasion, and will make you look bad to idiots that don't understand Disc mechanics or how to read a meter, especially as Disc tends to have lower spellpower and smaller heal numbers than Holy on top of the "invisible healing" of shields.

If you want to tank heal, be able to prevent damage, not have to worry as much about mana, enjoy the idea of the best, cheapest single target burst heal in the game (Penance), and still would like a little bit of AoE healing ability, Disc is a good spec for you. I suggest it as more new priest friendly as Holy, but the healing style isn't for everyone.

Once you actually hit 80, you have some options. Ideally, I would get some crafted gear scrounged up as best as possible (Wispcloak, and Ulduar-era crit+spirit pieces like the Cord of the White Dawn are decent places to start, and you can even invest in some ToC craftables if you have a ton of money or Triumph emblems on a main to burn). BoE epics from t7 and some from t8 content should be decently priced if you have some gold to burn and enough supply on your server. Basically, check the AH, and check on the mats for craftable pieces for an easy gear boost if you have the money to do so.

If you're poor, the prices on your server are outrageous, or you just don't want to spend that much gold, gear up the old fashioned way, like all us old people that hit 80 close to Wrath release. Start with level 80 normal dungeons. Make a list of all the blue gear that is an upgrade for you, and run until you get it, even if it's hard to find a group for the normal dungeons. Make a set with spirit, spellpower, and crit on it. Do not stack haste until you have enough regen to support it (i.e until you have access to fancy epix). Once you have a full set of this gear, run the easier Heroics (Violet Hold, Nexus, Utgarde Keep) and five man ToC regular. As you gain more confidence with the easier Heroics, move on to the more difficult ones, chasing after upgrades and more badges. Emblems are the key to better gear, even if the trickle from Heroics can be slow.

If you wish to be a PvE healer, and don't know a lot of people on the server, my suggestion is PUG. A lot. Eventually, you will have enough good experiences to fill a friends list and people will ask you back if they liked you and need a healer. Also remember that if you want to raid one day, a lot of raiders PUG Heroics when bored or wanting to do the daily as their guilds will not have enough tanks and healers to really go around.

I do feel bad that raiding has changed so much that t7 content is no longer relevant unless people are achievement chasing. You'll still see PUGs for 25 man Obsidian Sanctum on occasion, but for the most part, no one runs these instances. This is a shame, as Naxx, Sarth, and Malygos are all set up as starter instances that teach you the basics of raiding mechanics. Jumping straight from Heroics to Ulduar or ToC is of course possible, but it sounds like a much scarier transition, even with Emblem gear available.