I have a love/hate relationship with addons. Some are extremely helpful, some clutter the screen, some make life convenient until a patch breaks them. I think the important thing to remember about addons is that they are not required for you to play WoW.
This topic can turn into a monster, but lets look at it from the starting DPS point of view.
The first thing you need to do is to know why your DPS sucks. While a friend linking you (or that Pug that topped the charts) the meter for the last fight will give you some idea, it will not give you the real picture. Enter recount.
Recount is an addon that can provide a lot of information. Before the tooltips on the character sheet were updated to display a little more information about what the numbers meant, recount was the place I would look to see if I was missing with my abilities.
So step one is to download an addon that tells you where you stand DPS wise.
I think the following numbers will stay true until the end of Cata. These are the numbers you should be hitting to be on par with that content.
7K-9K – Dungeons – Greens and blues
10-12K – Herioc – Entry level – All blues
13-15K – Troll Heroics – T11 – Mostly Purples
16-18K – Firelands – HoT Heroics – T12 – iLvL 360+
19-22K – LFR – 1st half of Normal DS – iLvL 372+
23-28K – Normal DS – iLvL 380+
30-35K – Heroic DS – iLvL 390+
I am sure some people will think that those numbers are in the low side. I have seen people hit ridiculous numbers on greens and blues, and vice-versa, seen purpled out people not do more than 12K. I think the above are realistic numbers to look at.
Keep in mind that those are not dummy – static numbers, but sustained DPS. What that means is the DPS that you can sustain during a fight including moving and repositioning. A mage can hit 30K in the beginning of a fight blowing all his cooldowns, that does not mean that they are a 30K mage. A good way to look at meters is to look at Damage Done and see where your DPS stacks compared to other classes. So look at the numbers and compare them with the chart above but not as a high water mark, more of as an average.
If your numbers don’t seem to hit the above or even be close to it, there are also addons that can help you out.
One of the biggest problems with DPSers that are starting out is that they don’t know about uptime of dots and debuffs. Most classes have a debuff they need to keep up, some have several. Finding an addon that will display it for you will give you a constant reminder while in combat of keeping that debuff up. For a warrior for example, their shouts and rend are very necessary for the DPS to stay up. Druids with their Fairy Fire, DKs Diseases, etc. I use Power Auras for displaying what I need to keep up, and the cool think about it is that you can import auras from people that already built them. There are other addons like Tell Me When that might be a little easier to set up for a beginner. The WoW UI will display them for you, and it is now a little more configurable as well.
Keeping track of your Dots and Debuffs (as well as buffs) will affect your DPS greatly. Just keeping battle shout up is about 2K DPS for a warrior.
When starting out with addons a little way to cheat is to download an addon pack. The downside to going this route is that there might be too much going on, or it might be too different than the regular WoW UI. You also have to keep in mind that your computer has to be able to handle the added workload that more addons will put on it. I say to start out with just keep it simple and work with a couple of addons at a time.
All of this is not required to play the game, but if you want to raid and don’t use the tools you will certainly be at a disadvantage. While Blizzard has gone a lot further down the path of making things more configurable, addons are still a part of the raiding game.