How to target mobs
 

How do you target the mobs your tank is not attacking? Is there a way besides clicking and praying you finally target the other one(s)

Tab and watch for the blinky names?

Go into your options, look for the section on commands (or whatever it's called), there's a drop-down list that includes a Targeting section. Go there and make a hotkey for cycling through nearest mobs. Also make one for targeting the nearest mob.