I recently got my fire/ice blaster to 50 and this is what I found helpful. Rain of fire is great for oh snap that is a lot of mobs on me, RoF right on top of me, away they go. Frigid protection really slows down the mobs that get close. Once you get shiver you can slow lots of mobs to running in place. Ice patch is situationally useful, but always fun to watch. Best to drop it in doorways or choke points if you can.
I avoided pretty much all the melee powers. If I can't attack it from the air, I ain't killing it.