So I had thought this would be obvious, but I guess there are people who maybe don't notice it's a thing; but I played tank for the very first time in an MMO (minus minor WAR and NIN sub job leveling in XI) during one of the early Beta phases when they made GLA available. What I noticed as I got to around Toto-Rak, was that if I marked my current target and was good about switching targets as the mob was about to die, the runs became a lot smoother and most (but not all...) DPS figure it out and "attack the one with the big X above its head!".

For those that don't know, there are Marks that you can use to mark targets. The really cool thing, however, is that (like with the Emotes list) you can literally click the mark you want to use and drag it to your hotbar where you can then keybind it for fast and efficient mob targeting. I've found you really only need the one mark and using it to mark only your current target is enough. As a bonus, the big target itself can actually be clicked to allow easier manual targeting (at least for PC players) when you are trying target a mob inside a big pack of them. I'm sure an /assist command (which I don't know off the top of my head) would work similarly.

I now play with a friend who plays WAR and I play SCH. He marks targets as well. It's something all tanks (or at least SOMEONE in the group, but preferably the tank) should be doing.