Bien configurer ACT (anglais)

Install ACT and the FFXIV plugin for it.
Go in game and turn on all combat text in your battle tab (or any tab, but at least one should show everything.)
Go into the options for Encounter Culling, set the value high enough where it won't restart encounters during mechanics sections where no damage is happening (ex. Divebombs on Twintania). 30 Seconds is a reasonable number.
Go into Encounter Display options, and turn on both Encounter DPS, and DPS columns, and any others you like (ex. ToHit% for accuracy).
Go into the Plugin Options and turn on Combine Pets and make sure Limit Break is set to not be counted as damage for that player.
The 'DPS' column is basically DPS only during the time when you were actively performing actions, i.e. if you stop attacking and go run around in a circle, it will ignore that time. Encounter DPS is Damage Dealt over full fight duration, and is more is the more appropriate metric 99% of the time. Comparing your 'DPS' to 'Encounter DPS' is a good way to measure how much time you're spending dealing with mechanics; the farther apart those values are, the more time you spent not actually attacking the monster. 'DPS' will always be higher (or at best equal) to 'Encounter DPS'.