If you feel that some of these answers are off, please let me know so I can change them.
Q1. My DPS is too low, what am I doing wrong?
A. The most common issue is that your character's gear is not optimized according to your stat priority. There have been several threads where a warlock comes to the forums asking advice because they are only pulling 40k DPS. Upon checking their profile none of their gear is gemmed, enchanted, or reforged properly - if at all. Before asking what's wrong with your DPS, fix your gear. Get enchanted, gemmed, and reforged. This will go a long way to improving your DPS. If this is not your issue, see question 7.
Q2. What is the stat priority for my spec?
A. This varies depending on your gear level and spec, all of your gear should have Int on it, and your weapon should always have Spellpower, these are left out of the priorities to save space, but as a general rule, Int > SP > Everything else.
A1. Affliction: Hit (12% heroics, 15% LFR and normal Raids) > Haste (3043 or 4717 - whichever you can achieve without sacrificing too much mastery/hit) >= Mastery > Crit
*Note: In the source thread they say that keeping haste and mastery ratings nearly equal is beneficial. I want to clarify a bit what they are talking about. If you have 3043 haste rating, they are suggesting you also have as close to 3043 mastery rating as well, I suggest reading the entire thread to gain a better understanding of what they are talking about. When I sim my character I only see a difference of about 150 dps (which is statistically insignificant) when aiming for 4717 haste (4840 haste) and stacking mastery beyond that (5812) compared to stacking Haste (5377) and Mastery (5308) equally. This may scale better at higher gear levels though.
A2. Demo: Hit (12% Heroics, 15% LFR and normal raids) > Mastery >= Crit >= Haste.
A3. Destro: Hit (12% Heroics, 15% LFR and normal raids) > Mastery >= Crit >Haste
Q3. Simcraft says Hit rating is a DPS loss for me (Affliction), why are you insisting that I aim for the hit cap(s)?
A. Min-Maxing is important to world/realm first players. These players were progressing into heroic modes in 463 blues while the majority of us were still wiping on stone guards or trying to figure out how to start the quests in Dread Wastes at 89. Facing that content at such a low gear level they needed to use every advantage they could to beat the enrage timers or deal with these mechanics. It is not unheard of for these players to switch specs/gear sets/reforges or even hopping on another toon to down a boss as fast as possible. While hit rating is a DPS loss when trying to maximize your DPS, for the majority of players it is actually more beneficial to be hit capped while you learn the spec and encounters, and the majority of warlocks on these forums would agree.
Hit cap: The theoretical gain of not going for full hit is probably not worth it
It's been previously suggested as well as heavily defended by many users on this forum (including me) that it's not necessary to go for 15% hit. This suggestion should from now on not be used as a guideline for the general Warlock player.
The argument behind not being hit capped is that we will in theory not need it, mainly because of how Pandemic makes us most of the time not refresh dots before they expire so they would rarely drop completely if we missed them. SimCraft suggests that we'll gain quite a lot by ignoring hit, however this doesn't work as well in practice.
If we don't hit cap we will sometimes not be able refresh the dots with procs when we want to. Not only will we waste globals on misses but also will we get a lower uptime on the said buffed dots and have to start channeling Malefic Grasp with these procs up later. It just puts us behind a lot.
Another argument is that reacting to misses might take focus away from performing the mechanics of the encounter. We're only human after all.
The best argument for getting full hit cap might come from checking what the top Warlocks have done since the release of MoP. Even back in MSV most of the Warlocks in the hardcore progression guilds went for full hit cap. I think we can assume they are all at the skill level of being able to react to misses. Still they didn't think it was worth it and even if it might not be backed up theoretically we should probably assume they have good reasons for sticking to the hit cap.
Finally, it's been pointed out that as we get closer to full T14 BiS gear we are not losing more DPS from acquiring the hit cap. In other words it's likely that the value of hit gets higher with better gear and it's safe to assume that the gain of not reaching the cap will be very low in future tiers.
Q4. What are the haste soft caps?
A1. For Demo and Destro there are no specific caps to haste that you need to aim for as haste remains beneficial even after you surpass the attainable soft caps, however there are points where haste becomes less beneficial than the stat priorities listed in question 2 above (like when you pass a haste threshold). Use simcraft to find out the weights for your gear level. If you are still curious where these Haste Thresholds are, the spreadsheet I linked below has these values.
A2a. For Affliction there are several, the ratings apply to all races except for goblins who have a racial that gives them 3% spell haste - for goblins check the google spreadsheet for the rating you need. The first attainable rating is 3043 (12.52%). At this rating with a 5% spell haste buff, you will add 1 additional tick to UA and corruption, and 2 additional ticks to Agony.
A2b. The 2nd attainable rating is 4198. This rating will give you an extra 4 ticks to UA when heroism/blood lust is popped, and will also give you the extra 4 ticks of UA every time you hit Dark Soul: Misery while not under the effects of heroism.
A2c. The 3rd attainable rating for affliction is 4717 (16.65%). This rating will give you 2 additional ticks of corruption.
There are several other breakpoints you should be aware of for affliction, for a complete list visit the following sites:
Q5. Expertise on Locks? Really?
A. When MoP was launched, the hit/expertise caps for melee changed. The hit required to cap was reduced from 8% to 7.5%, and expertise required to soft cap was changed to 7.5%. To solve the problem of paladins and enh shamans who needed to also be spell hit capped spell hit was added as a 1% melee exp = 1% spell hit and 1% melee hit = 1% spell hit. As a result all casters can benefit from expertise for spell hit. It is also worth noting that Int+Hit gems are Purple (red/blue socket bonus), and Mastery/Crit/Haste+Expertise are Orange (red/yellow sockets).
Q6. Where can I find guides on how to play my class?
The following guides I am posting in lieu of the sticky threads in this forum because A.) they are maintained better/more often, and B.) they actually have stickies in the MMO-Champion Warlock forums.
A1. Affliction: http://www.mmo-champion.com/threads/1179309-MoP-Affliction-Warlock-Guide-and-First-Week-Gear-List
A2. Demo: http://www.mmo-champion.com/threads/1248982-5-1-Demonology-Warlock-Guide
A3. Destro: http://www.mmo-champion.com/threads/1179320-MoP-Destruction-Warlock-Guide-and-First-Week-Gear-List - it has been pointed out that this thread is a bit dated, the guide below was provided by Methalos
Q7. My DPS sucks, what should I do?
A. First, see question 1. If this is not your issue (or you were sent here from question 1) read on. Upload a parse of a LFR or normal raid you have recently done to World of Logs than post that along with any specific questions you have in either a new thread on these forums or in the MMO-Champion "Fix My DPS" thread found here: http://www.mmo-champion.com/threads/671130-Help-Me!-The-quot-Fix-My-DPS-quot-Thread-(Read-first-post-before-posting)
I would suggest that going to MMO-Champion may be more beneficial because they have quite a few Warlocks that frequent that thread that are top 100 locks and you are less likely to get misleading information (although it is still possible).
Q8. Everyone keeps telling me to run Simcraft, how?
A. This guide is not very comprehensive, and is a bit dated (over a year old) however it has all of the pertinent information you need to simulate your character (*Note, he says use simcqt.exe - you will not find this file in the windows version any longer, it is now called SimulationCraft.exe, and the overrides for extra iterations is no longer needed as those have been added to the global options drop down (100k iterations still needs an override, but 50k iterations was added)): http://www.mmo-champion.com/threads/826823-SimCraft-Andromalia-s-Howto-SimulationCraft-Thread
Q9. Pandemic means we can keep our dots up 100% so whats the point in reaching haste thresholds for additional ticks if the dot never drops off? We will never see that additional tick will we?
A. This was an extreme example of how pandemic and haste work with each other. TL;DR - haste increases the FREQUENCY of the ticks (how often each each dot ticks)
Think of it this way, a boss has an ability, lets call it Rain of Blades. This ability does 45,000 damage to all raid members every 0.5 seconds, and lasts 6 seconds (hitting 12 times), this is a total of 540,000 damage over 6 seconds. Lets assume this boss just stands there and casts nothing but Rain of Blades for 5 minutes and has Pandemic meaning this dot never falls off. Over the course of 5 minutes, this ability will tick 600 times, meaning the boss does 27 million damage to every raid member with this ability.
Now lets give the boss some haste, enough haste to add 3 ticks onto this ability. With this haste, the tool tip for Rain of Blades now reads "Inflicts 45,000 damage to all raid members every 0.4 seconds, and lasts 6 seconds", (hitting 15 times). Now the boss is doing 675,000 damage over 6 seconds. Over the course of 5 minutes, this ability now hits 750 times, meaning the boss does 33.75 million damage to every raid member with this ability.
In gaining that haste, even though the dot never drops off the boss is doing 6.75 million more damage, to each raid member. In a 10 man raid, that's 67.5 million more damage. In a 25 man raid that's 168.75 million more damage.
Even with pandemic and 100% up time, the frequency of your ticks matter, this is not debatable.
Now when you are just below a haste threshold where getting a bit more would add an additional tick, you should also note the duration of the dot, as this becomes important when multi-dotting or on fights like Feng where timing refreshes becomes important because of mechanics like Epicenter. Take for example Corruption. At 2302 haste rating (non-goblin without the +5% spell haste), corruption only lasts 17.07 seconds. At 2373 (closest I could get to the 2367 threshold) it lasts 18.94 seconds. So not only did I gain an extra tick of corruption by adding 71 haste, I also increased the time corruption would be up with pandemic by 2.8 seconds, which is substantial. The same thing happens at 4700 and 4717 haste rating with a 5% spell haste buff. You gain nearly 3 seconds on corruption just by gaining 17 haste.
I can't think of any other questions to add at the moment, as this covers the majority of the questions I have seen in regards to PVE. If anyone wants to add anything to this, just reply with the question and answer, a source for the answer is not required, but it may add a bit more weight to the validity of your answer.
Updated stat priority for Destro, added Methalos' guide for destro.