Swiftcast and Raise is a godsent combo. As well as Swiftcast and Medica II if you know you won't be needing to raise anytime soon. Usually SCH and SMN are on raise duty in parties because of their MP regenerating skills, but don't assume they will raise.

Presence of Mind and Divine Seal are both your friend, especially when you need to spurt heal.

Benediction is your hail-mary before death ability but takes a bit to actually enact so try to remember that before using it.

Hit Shrouds of Saints after using about 1k-1.5k MP to make sure it will be off cooldown when you need it.

If you are DPSing, opening with Swiftcast and Holy is good, then longcast Holy spams. Just remember to use Shroud of Saints after Holy spamming to lose your enmity gained and to regen your MP.

Don't stand next to Smitten in Ifrit HM, she always gets the cracks.