Rankings are based on the following abilitiy priorities:

1) Frost Bomb to proc Brain Freeze
2) Frozen Orb to proc Fingers of Frost
3) Frostbolt to reach 3 stacks of debuff
4) Freeze (Water Elemental Ability) to proc Fingers of Frost
5) Frostfire Bolt on Brain Freeze proc
6) Ice Lance on Fingers of Frost proc
7) Frostbolt when nothing else to do

Also use these as often as possible!:

1) Alter Time
2) Mirror Image
3) Icy Veins

Water Elemental is up
Frost Armor is active

Stat Importance

15% Hit > Intellect > Haste > Crit > Mastery