I'm not big on fancy text formatting, so expect this guide to be a little, meh.
This guide is a first in a series of guides I will be writing for people who have bought/aquired an account that they themselves did not level to its cap. This guides aim is to give the reader a more complete understanding of their class. They are completely original, and I wrote every bit of it from experience and research. They are to only be posted on MMOwned unless I have said other wise.
Now lets get started.
Section One (part one) : Priests, and what they do
Priest primarily are known as a healing class, due to the two trees they posses that have amazing healing spells, and benifits. However, Shadow Priests are known to be amazing DPS as well, and can compete with locks even on their Dots, and the 15% Shadow damage you gain in shadow form is a plus.
Priests unfortunately are stuck with cloth gear, making us more "squishy" than the competing healing classes, Shamans, Druids, and Paladins. However, we do have Inner fire which is a great armour buff.
Section One (part two) : Priests and their races
Alliance side 4 races can be priests, and all have their respected racials. Dwarfs have Stone form, which is usefull in PvP, but not entirely usefull in most situations. They also have "Find Treasure" which is negligable considering the high use of things like "Quest Helper". In short it allows you to track things like chests. They also have frost resistance, which is usefull, but not a race decider.
Humans in my opinion are the second best race for priests, they have The Human Spirit, which adds 3% spirit, and stacks with other spirit increases. Diplomacy gives you 10% more reputation, which is a bonus when farming rep for a mount, or what have you. Everyman for himself is basically a "Medallion of The Alliance", and allows you to despell a movement impairing effect, whether it be a fear, or a stun. Allows you to remove that trinket in place of one to further increase your stats. Perception allows you to see stealthed mobs, players, as if you were one level higher. Slightly usefull for PvP.
Nightelfs in my opinion are the best race to select for your priest. Shadow meld, is essentially a vanish now, considering it drops you from combat immediately, and is good as a second fade, or a gank deflection. And now with the newest patch, the cooldown starts as soon as it procs, so you can let the CD refresh while still stealthed. Quickness adds a 2% dodge, so you get hit less often, and is nolonger disabled by a stun. Wisp Spirit turns you into a wisp when you die. Not too usefull, but you do get back to your body a little bit faster. Nature Resistance grants you a 2% chance to avoid nature damage.
Space Cows are IMO the worst class to pick for your priest, and I wont explain their mechanics.
Horde have 3 races that can be priests, all IMO decent for the roll.
Blood elfs have a few nice racials, such as arcane torrent which silences all enemies within 8 yards for 2 seconds, and grants you 3% of your mana back. Magic resistance grants you a 2% chance to avoid Spells, and arcane affinity increases your enchanting skill by 10, great because enchanting is a very costy profession, and has great rewards.
Trolls IMO are the best horde priest class due to 10% casting speed, and 30% when at 40% or below health. Regeneration grants you 10% + to your health regen rate, but isn't too usefull due to our already low hp regen. Da voodoo Shuffle is a 15% decrease to movement impairing effects, and is usefull if your trinket is on CD. Beastslaying gives you 5% more damage done to beasts, 'nuff said.
Undead have Will of The forsaken, essentially a copy of the human racial, but this only rids you of charms, fears, and sleep. Not stuns. Cannibalize reduces down time when grinding, farming, by allowing you to eat the ones you have downed for health. (7% every 2 seconds for 10 seconds). Underwater breathing allows you 10 minutes, as opposed to 2 minutes, of underwater breathing. And lastly shadow resistance gives you a 2% chance to avoid shadow damage.
Part Two : Gearing Your New Priest
Intellect is how much mana you have, the more mana, the more you can cast. The more you can cast, the more you can heal, and the better your DPS is. Nothing is wrong with that eh? For every point of Intell, you gain 10 to your total mana bar. Try and get as much intellect out of you gear, while never sacrificing Spirit. Spirit is one of the most important, if not the most important priest stat. Spirit and MP5 is your mana regen rate, if you go OOM in a raid, you are usless. Well, at least until you can get an innervate, but who wants to rely on someone else, when so many people (IE The Tank) has to rely on you? Gear for this as much as possible. Spell Crit is extremely important for various reasons. Pre patch 3.0 the only shadow spells that could crit were mind blast, and Shadow Word: Death, making it almost negligible for shadow priests, but now mind flay can crit every tick, and that increased the damage priests can do by a bit. Healing gains alot from crits as well, especially with the buff you give the target with the talent "Inspiration" on the disc tree which grants them 25% percent more armour. And with Holy Concentration, and imp holy concentration you can gain either clear casting after a crit (Allows your next heal to complete with no mana cost) and with Imp, you gain 30% spell haste.
Spell power is the amount of damage you can do with your spells, or the amount of healing you can deal. The more the better, around 70 1k is optimal, 800 is accepted. At 80, expect around 1.5-7k. Hit rating increases the chance your enemies wont resist your offensive spell (Healing does not apply to this stat) you want to max out your hit rating as much as possible, considering you want all of your spells to hit the enemy. At 70 12.6 hit = 1% + chance they wont resist. Shadow focus, and misery on the shadow tree help your hit rating. Spell penetration is much like hit rating, 'cept it reduces the enemies resistance to the spell. Useless in PVE IMO.
My haste explanation is a direct copy from a guide a read a while back, because I can't think of a better way to explain it. "Haste rating decreases the amount of time that it takes to cast a spell, and it reduces the channeling time for channeled spells. It also can reduce the GCD down to a minimum of 1 second, although you need a realistically unobtainable amount of haste (785) to reach that point.
To determine the casting time of a spell based on a certain amount of haste, you must first calculate the spell haste percent:
% Spell Haste = (Spell Haste Rating / 15.7)
Then you use the following formula to determine the new casting time. For note, if you have a talent that reduces the cast time of a spell (ex: Divine Fury) you should use the improved cast time for the base casting time value.
New Casting Time = (Base Casting Time)/(1 + (% Spell Haste / 100))
For shadow priests, after you have around 1400 shadow damage, one point of haste rating is equivalent to one additional point of damage. There isn't as clear of a point where haste becomes valuable for holy priests, but in general, being able to pump out heals faster is a good thing." -credit goes to the original poster of that quote.
Part 3 : Speccing your new Priest
So you just got your priest, you know what gear to get, what to improve on stat wise, how do I spec him? Is he already specced correctly? Well, as with all specs, it all depends on what you want to do. The PvP spec of choice is going to be disc considering its spirit increase, and intellect talents. A spec would generally look something like this Talent Calculator - World of Warcraft As far as PvE disc priests, I don'thave much to say but "Good luck", as a DPS you aren't really built for PvE, however, one of the best healing specs is a Disc one. If you must, this http://www.wowhead.com/?talent=bVIbuuxtM0oifRtcxuc is a pretty good PvE disc set up, your gear should focus primaraly on Spell power, and crit. Spirit and haste are needed, but not more important.
For healing there is two ways you can go in the talent tree, holy healing http://www.wowhead.com/?talent=bVsbzhbZcxtccMqiuVhot which in my opinion is a bad idea, with the recent removal of downranking. Or http://www.wowhead.com/?talent=bVcbuhxtMLoifRt0x disc healing. Which IMO is better for most situations. While holy priests have CoH, and Guardian spirit, disc priests can heal faster, more efficiently, and have more spirit. You do lose a little healing power by moving to disc, but it's less that 500 points. Now for DPS/leveling you're going to want to go with the shadow spec, a good one can be found here http://www.wowhead.com/?talent=bVcbzhZZG0fVRfzciqczAo, and I'll talk about it more later.
Part Four : Spell Rotation
For spell rotations, I'm going to start with my favorite spec, shadow priests.
Assuming you followed the above spec http://www.wowhead.com/?talent=bVcbzhZZG0fVRfzciqczAo you should have mind flay, shadowform, and vampiric emprace added to your spell book.
For bosses, you'll want to do Devouring Plague > Vampiric Touch > Mind Blast > ShadowWordeath > ShadowWord:Pain. Why is SWP so far on the list? So it can get the most out of shadow weaving, because you casted 4 shadow spells before it. Make sure to keep VT, and DP up as much as possible, and if the group is having a hard time, toss up a Vampiric embrace up every once in a while.
For trash, just DP>VT>MB>MindFlay, until dead. Shadow word pain would be useless as they will be dead long before your shield expires.
(The rest is under construction, I'm having to leave the computer I'm at, so this will be updated, and finished soon.)