It depends, but in general I usually let regen and divine benson do my work for me so I can dps more, and then when the tank gets to around 50% I'll start using instant casts like tetragramaton/aflictus solis or however it's spelled to use up as little time healing as I can so I can dps. I use assize liberally for mostly DPS purposes.

If the tank is pulling wall to wall I'll use asylum and cure 2 spams along with the stuff I said above.

For trials and raids, I'll use medica 2 as much as I can without sacrificing MP and dps, as having it up constantly is unnecessary and wastes MP.