Hammer of Wrath > Crusader Strike > Judgement of Light > Divine Storm > Consecration > Exorcism
Basically, you hit whatever ability is off cooldown and at the top of the list.
For the first 80% of the fight--where Hammer of Wrath is not available--you can simplify the ability list using two macros:
/castsequence reset=4 Crusader Strike,Judgement of Light,Crusader Strike
/castsequence reset=10 Divine Storm,Consecration
Your priority list now becomes:
Macro 1:Single-target > Macro 2:AoE > Exorcism
If the first macro is on cooldown, hit the second. If both are on cooldown, and Art of War is up, hit Exorcism.
This scheme is identical to optimal FCFS, but only uses 3 buttons instead of 5, so you might find it easier to use. It also has the advantage that if you can't AoE (for example, Crowd Control is being used), you can just ignore Macro 2.
Once Hammer of Wrath comes into play, the above system breaks down. However, there is another sequence which comes very close to optimal FCFS play. You lose about 1 second out of every 24 seconds of DPS, which is about a 4% loss from perfect play. However, 2 buttons are a lot easier to press than 6, so you might find that you come out ahead.
Macro 3: Execute
/castsequence reset=target Hammer of Wrath,Crusader Strike,Judgement of Light,Divine Storm,Hammer of Wrath,Crusader Strike,Consecration
The priority list becomes:
Macro 3:Execute > Exorcism
As before, if Macro 3 is on cooldown and Art of War is up, pop Exorcism.