Raise your game with Recount!
Check out the video guide at ESO Traveler
Recount is a handy addon that records your DPS (Damage Per Second) and HPS (Healing Per Second). If used correctly it can help you work out the kinks in your build. If abused it can make you look like an elitist jerk.
The basic premise is simple. Recount records your damage output, shows your overall DPS and HPS, and itemizes a list of abilities. Based on this data you can change and tweak your build and rotation (the order of abilities that produces the most output) so that you are killing mobs and healing allies as efficiently as possible.
While recount is a useful tool, it can be abused. Don't become a hopeless number cruncher who constantly posts results in chat and chides other players for their poor DPS. Ignoring game mechanics to produce optimal DPS is also a no no. Good raid leaders will tell you that staying out of the red is more important than DPS.
You can download recount here