There are few from me, some already mentioned:
- trait blue, but use two yellow line traits to make anthems longer and their cooldown shorter.
- focus on healing only, but even at the very beginning do not forget to tier up you ballads. If you are confident enough or you are bored, you may try some anthem buffs or even damaging skills.
- unless there is a specific need for that, do not heal anybody before the start or in the first second of a fight. Even the best tank need some seconds to grab and maintain aggro. And usually can survive some time without heals. It's not that bad if there is only one mob/boss but a stray mob aggroed on a healer at the start may make an encounter quite messy.
- there are already mentioned tricks about single target healing - you can use them. One additional: a nice quick heal is Chord of Salvation followed immediately by Soliloquy of Spirit. SS cuts an animation of CS and shortens a time to use the next skill.
So, if somebody needs a fast huge heal you may try a combo: Chord of Salvation -> Soliloquy of Spirit -> Anthem of the Third Age (I assume that you have all ballads up) -> Coda -> Bolster Courage.
Warden(85), Minstrel(85), Rune-Keeper(85), Burglar(85), Captain(85), Hunter(85)