There is no rotation for frost. Keep throwing frost bolts until you can deep freeze then cast that and throw 2 ice lances. Whenever your icelance spell glows, cast it until it stops glowing (usually 2 casts only) and cast frostfire when it lights up.
So this is a really good example of what Blizzard wanted to accomplish with PvE rotations in Cataclysm: you could just button-mash, like this guy is advocating, and do OK. Or, you can play the spec properly, which is going to be more complicated, and do better.
This is the optimal priority list we've been able to nail down so far in simulation:
The key idea here is that you keep a charge of Fingers of Frost banked so that it's ready when Deep Freeze comes off cooldown or Brain Freeze procs. You only use Ice Lance if:
1) You have two FOF charges, casting it once to bring you down to one charge
2) Pet Freeze is about to come off cooldown, in which case you burn off any FOF charges with Ice Lance, cast Freeze to bring you back up to two, and Ice Lance one more to bring it back to one