This is how I was playing THM in the beta at level 35.

Blizzard I to get Umbral Ice active
Thunder II then Thunder I (this way they both wear off at the same time)
Transpose
Fire IIIx3
Transpose

and repeat. Sleep the adds in pulls, Scathe to kill steal finish a target off. As for sub abilities, I used

Cure and Raise
Blood for Blood > Raging Stikes > Quelling Stikes > Internal Release (I activated them in this order since Blood for Blood and Raging Stikes last for 20secs, while the last two last for 15.)

So it's not really just spamming Fire and Blizzard if you are actually trying to play the class.