Ellay had/has a video in the movie section, which was a video tutorial. It is for arena, but is pre Wrath, so some things have changed and some are the same.

For the original three arena's it mentioned where to stand and why.

He prioritized DPS as the first targets to take out.
Mainly because as a boxer they were the most threat to him.

In most of his video's, it is the DPS switch which gets the opponents, especially at higher ratings.
Put some DPS on one, then switch to another quickly and either burst them down or DPS a little and burst the first target down.
Using target=focus type macro's you don't even have to target the burst target, just need Line of Sight.