Order of Kills and Target
Guild Wars 2 loves innovation-like any good MMORPG should. Because of this, mobs react differently than mobs in any other MMORPG that you would expect to play. In GW2 they try to help their teammates, can heal each other, etcetera. Because of this, it makes it crucial to establish a kill order and plan before engaging a group of targets. For example, killing Ascalonian monks in Ascalonian caves, then Mesmers and Elementalists, is a popular kill plan in Ascalonian cavern.
For obvious reasons, sometimes it may be necessary to repeatedly engage the group multiple times before finding the optimal kill order. In GW2, it’s not always about killing casters first. But hey! It’s all part of the fun o’ the game!
Once you have a plan on who to kill first, then you will want to make a more specific plan, and assign someone to call out a target. Fortunately, this is made super-easy with Guild Wars 2, and they even have hotkeys for it. To call a target, you have to first have them targeted. Then press [Ctrl] + [T] this will make an obnoxious and obvious flag above the target, and allow for other party members to easily recognize which mob to focus. From there, the party can press [T] to automatically target that same target.
Focusing down mobs will make dungeons easier and make the dungeon enjoyable, so by all means do it!