If you are asking this question, it is safe to say that you feel as if you're not playing your class to its potential. Dealing damage, in World of Warcraft, can be very easy on the surface but what does it take to do better DPS in WoW? What does it take to do high DPS?
Assuming that you have already visited a class guide, your character is gemmed, enchanted and reforged properly, but you're not matching or coming close to the DPS that other players of your class are pulling off. You look at these players and notice they have very similar gear as you are but they are doing significantly better. What gives?
There are a few tips and tricks that I will reveal later on, but I would like to emphasize on one key to doing better DPS in WoW. Changing how you think about DPS is extremely important to your goals of becoming a better damage dealer on the grand scale of things. You need to think about DPS and damage done in a very simple mindset. DPS means "Damage Per Pecond", dealing a certain amount of damage every one second. You must think about one thing, "How much damage can I put out during an exact time frame per second?". For example, if a boss encounter has a hard enrage timer of five minutes, then it's safe to assume that you, as an individual, need to deal as much damage as possible in 300 seconds.
So how do you do better DPS while under the mind set mentioned above? There are a few factors in obtaining better DPS which include key binding, "ABCs", button mashing or "spamming", "cooldown" usage, utilizing trinkets and positioning. All of these factors combined contribute greatly to a player's success in a raiding environment and ultimately lead to your goal of doing better DPS.
Let's talk about key binding. Key binding involves assigning hotkeys to certain abilities and spells to your keyboard for easy access and execution. Assigning crucial spells such as "Fireball" or "Arcane Shot" to your action bars can greatly improve your DPS by making sure they are bound to a very easy-to-push key on your keyboard. Assigning your "Fireball" spell to the "1" key allows you to rest your hand on the left side of the keyboard (with your movement keys) and provides easy access to the spell. With enough practice, you can memorize key binds for all of your spell's hot keys which in return, allows you to button mashing or "spam" your spells faster, which I will explain in detail later.
The "ABC" of raiding is simply referred as "Always-Be-Casting". This is a universal rule for dealing damage in WoW. The idea behind this rule is that if you are always casting something, you are doing more damage overall than you would be if you are not casting at all. The idea is simple, but it applies to movement and latency, which I will be explaining later on. Just remember that you need to keep your ABC mindset in full force during an encounter.
So your key binds are all setup and memorized, let's get into button mashing or "spamming". This style of playing is a universal "skill" for each role in the game. Players mash their keys for a very simple reason, which is latency. Latency, in basic terms, is the amount of time which your computer or "client" sends information to Blizzard or the "server" and then sends it back to your client. It goes without saying, having a lower latency means you send and receive information between yourself and the WoW servers faster. Players with a lower latency, tend to have an excellent internet connection and live closer to the data center where your realm is located. So, what we can determine from this information is that having a lower latency is a clear advantage to obtaining better DPS.
Players tend to button mash their keys to battle latency problems. When you press an ability, you invoke what is called a Global Cooldown or "GCD". This global cooldown is indicated by the small "shadowed timer" that you can see after hitting an ability, this small mechanic is to prevent players from casting instant cast spells in rapid succession and to help combat latency. The global cooldown is exactly 1.5 seconds. This small cooldown is what allows players to maximize DPS by being able to queue up or move your finger to the next spell in the rotation or priority and have it ready to cast when the GCD is over. Mashing your keys in between the GCD assures that your spell is being cast at the fastest time humanly possible, after factoring in latency. Learning rotations and priority systems for your class, mixed in with button mashing, will reduce the amount of error involved with latency and allow you to obtain higher DPS during an encounter.
Cooldowns, referring to spells and abilities that alter your damage output, can make the biggest difference between an average raider and an excellent raider. These abilities are termed as "cooldowns" because the cooldowns associated with the ability are significant. Allow me to use a very basic example of a generic cooldown that you may find in the game. This ability increases all damage by 40%, lasts for twenty seconds and has a three minute cooldown. It's obvious that this ability is quite powerful and you obviously want to use it. The biggest question you can ask is "when?". Referring to what I mentioned initially, DPS involves doing the most damage per second in a certain time frame. Let's say our example boss fight is five minutes long, your most optimal use of this specific cooldown would be to use it at the very start of the encounter and again at the three minute mark of the encounter. Doing this, you are effectively putting out 40 seconds of 40% increased damage in a 500 second time frame. Many damage dealers like to line up cooldowns with Bloodlust/Time Warp/ Heroism as well. If you stack a 40% damage ability with 30% haste, you are spending 20 seconds of that haste buff mixed with 40% damage. There are many different ways to get the most out of a cooldown which will change from fight to fight, it will be up to you to decide what is best. Using this type of thinking during an encounter, will allow you to make that decision easier, which builds you up into an experienced raider.
A small, yet important part of cooldown usage is also using trinkets properly. Many trinkets are used to boost damage significantly for a short period of time. Let us use the example of the 40% CD, the 30% haste and a trinket proc. This example trinket is a twenty thousand intellect boost for 20 seconds. It's definitely the dream trinket for your class. It has the same duration as your 40% damage ability and can be used for a good chunk of Time Warp. These trinkets usually have an internal cooldown or "ICD" which means that the trinket can not activate again until the ICD is over. The most important part of trinket usage is "lining up" huge damage abilities, trinket activations or "procs" and other buffs such as Time Warp, to increase the amount of damage you do in a twenty second window. An average raider will just use abilities on cooldown, while an experienced raider will "line up" all the damage boosts possible during an encounter.
Positioning and movement is another huge factor for better DPS during an encounter. Planning your positioning in an encounter before hand, leads into easier movement if you absolutely must. These two things tie in greatly to how many encounter mechanics are involved and how you deal with them. Let's say, for example, that a boss mechanic involves the boss placing a huge circle of death directly on a player, you specifically. You have three seconds to move from this circle or you die instantly. Imagine that you are playing a mage, your options include running out of the circle, using instant cast spells (ABC) while moving out, or you can use the spell "Blink" which sends you forward a short distance instantly. An average raider will definitely run out of the circle while an experienced raider will use one GCD, to blink out of danger and continue casting high priority, high damage spells. This is a very simple example of the type of thinking you need to develop while raiding and is not always the best answer. Again, it is up to you to decide the best course of action during an encounter.
So let us combine all the factors that I have mentioned above and mix them all together. Combining positioning, procs, cooldown usage, ABC and latency, you will be casting the most abilities possible in a certain time frame, leading to the highest DPS you are capable of executing. Keeping all these in mind will separate an average raider from an experienced raider. Once you practice and execute these factors, it will come natural to you, which in return will net even higher DPS since you do not need to put as much thought into it. You'll be able to focus on the encounters themselves which will lead into better positioning and movement planning.
I'm going to make a brief mention of a word you may or may not have heard while searching around class forums or guides, which is "simcraft" or simulation. Simulation is exactly what it means. Software designed around many different factors and near perfect execution to determine the highest theoretical DPS for a class in a specific time frame. These simulations can be programmed to not exhibit human error. My advice, if you get into "simming" your character, would be to look up a guide to make sure your simulation is configured correctly. After a correct configuration, you'll need to understand that your goal should be obtaining reasonable DPS compared to the simulation and not the exact simulation output. As I mentioned, these simulations are programmed (but not always) to exhibit no human error and perfect latency, so do not feel bad if you do not reach perfect results. If you do manage to reach near perfect results, good on you, but just remember that it isn't a realistic goal. Take into consideration that not every boss is the same and you definitely wont be dealing damage at maximum potential for five minutes straight on one target.
In conclusion, taking everything into consideration, your damage dealing capabilities will definitely improve over time, All of these ideas may seem daunting at first, but I assure you that every raider has gone through similar problems that you may have and improved through practice and hard work, just like anything else.
I wish you good luck out there, fellow raider. Remember to have fun.