Open with foe and battle voice.

Are deaths likely? keep some mp for ballad incase healers run low. Paeon a physical dps if he dies and his invigorate is on cooldown. Paeon a tank as soon as he is resurrected.

Is it a longish fight and do you have melee dps? Be prepared to be asked to play paeon.

Is there an aoe section and are u with physical dps? Paeon.

This will all come from experience really. You should foe requiem as much as possible while taking everyones tp/mp now/later in the fight into consideration.

If you are in a static this is even easier. You get used to the timings that party members need tp, or even mp.