As already said, for single target it's Aero III --> Aero II --> (Aero if in a situation listed by SecretCrowds above) --> Stone III spam (you can use Precence of Mind to boost this!).

For AoE DPS, Aero III --> Holy spam --> Assize for extra DPS and MP (You can also begin with Swiftcast Holy to give yourself some breathing room, then Aero III and more Holy).

DreamWeaver already suggested a good macro for you. Remember to use your Divine Seal regen, Eye for an Eye and Asylum to create yourself more DPS room (and Assize and Shroud of Saints on every cooldown for MP).

To add to those "when to use Aero I", you can also use it when you're switching away from Cleric Stance in addition to the situations already listed. But try not to push monsters around too much.