I suggest you to be near the ranged damages dealer.
If you aggro a monster and a ranged dps aggro an other too, the 2 ennemies will go in the same spot. It will be easier to the tank to take them back.

But don't be exactly on them because of the area damages (oranges circles on the floor).
If you're in an area damage spell that target someone else, you'll have to move too.