I've noticed that alot of Priests panic during a battle and use SoL (Surge of Light) on a Tank with a yellow Health Bar when they could've just used Revitalize and Heal. And the fact that a few Priests generate unintentional hate by casting unnecessary poison/petal rain spells on a certain monster when they could've just leaved it alone and conserved their mana for healing.*Sigh*That's why its nerve-wracking to be a tank. You never know when a healer screws the healing game.
Without proper guidance as a first time healer i guess that is unavoidable.So as a healer remember that on a raid boss you need to think conservative as your mp will run out. some battles take longer then others as well making it even more important to conserve mp because as soon as you run out of mp the raid is over.also remember to keep an eye on your self as well as some bosses send out skills that do major damage to the other players and not just the tank.take Noxxara (HT boss) as an example it summons poison patches on the ground, make sure to move out of these.you rarely need to use any skills apart from revit and heal. sometimes the emerald shield can be useful, like when two players are heavy damaged at the same time, put EM on the damage dealer and heal the tank first.the rest is experience i guess.
There was a time in the Snowpit when I was tanking as priest (Ironic, isn't it? I have a bunch of Tank equip since I always ge tthem from Dungeons XD) And asked the 2 other priests to revit or heal me. I was doing a quest for them, allowing them to petal rain the monster as a finishing move. They keep spamming Revitalize on me when they just casted a Revit on me because I received damage..Or the fact that they use SoL on undead when they could've just used Petal Rain_ _ \(-.-)/