As far as endgame content goes... Be ready to always hit your Benediction and your Swiftcast when absolutely needed.
You need to learn how much damage your tank receives AS WELL AS how much your other healer is actually healing. Sometimes you need to adjust with different healing partners.

A lot of mistakes I see newbies make is trying to proc that Freecure too much, and missing a Cure II when the tank needs it.
But this isn't to say you shouldn't be using Cure 1! If you spam Cure II, YOU WILL RUN OF MP.

Beware of OVERHEALING! It's a killer!