Drop down 2 blizzards and a slow time to make sure no one will be getting to you any time soon. While the blizzards are doing their damage, start to pick off mobs with ray of frost spam. If anyone gets close, stun them with Wave of Force.
Ray of frost will be doing 297% weapon damage and you can spam it as long as you want :)
Blizzard will do 337% over 6 seconds. Once you hit 60 I would probably change to unrelenting storm for more damage.
Another neat thing about this build is that you can pretty much start it around lvl 27/30.