Take it a step further and Hot Key your assist command. Then you just target
the primary tank in your party and hit your hotkey and you will automatically
target and attack whatever they are fighting. OR, since we bards tend to do
most of the fetching, you convince your party members to create a hotkey and
have you targeted when you leave to fetch and when you return they hit their
hotkey and will target whichever monster you selected (helps in crowded dungeons
and various other situations).

(Hotkeys are created by right-clicking on any of your social buttons and then
editing it to contain a title and command or text or both. Hotkeys can probably
only be created from the main interface [small window] screen.)

Narcissus of Povar