I haven't run any numbers on this macro, but it helped boost my dps from just frostbolt spam.

I always put focus magic on the boomkin, then this rotation helps hit the brain freeze talent procs. I started adding in the ice lances just because they're instant and every now and then the target is frozen.

/target [target=focustarget,nomod]
/castsequence reset=combat frostbolt, frostbolt, ice lance, frostfire bolt, frostfire bolt, ice lance
/cast icy veins
/use 13
/use 14

Atm I don't have any other ideas for boosting frost dps.