Originally Posted by
Cactrot
Some basic general advice is practice practice practice. That will help you get used to your priority. Another thing is to set up your UI so you can see everything you need to see easily and quickly. How that's done will vary from person to person, but play around and get to it. When your information is consolidated it's easier to keep track of it all.
Finally, try keybinding. Your DPS will probably go down at first as you won't be used to it, and it will take time to get used to. However, in the long run it will help your DPS. Your mouse should be free for controlling movement, changing targets, and mouseover macros for damaging adds without swapping targets.