Don't overheal. Use Regen when you get it. I use it all the time, after the tank has pulled the enemies so that they don't go running all to myself though.

If you're still learning don't feel bad if you just sit there for the duration of the fight, only healing. I had to do that the first time I healed dungeons. Soon you'll be able to learn when to DPS and when to heal but for now, don't feel bad just watching and throwing out heals when someone gets low.

Use Cure unless heavy damage was taken, then it's time for Cure II. Don't bother with Cure II on the DPS unless they've got some serious hurts.

Also due to Brayflox and its love of poison on the last boss you are gonna have a hard time with mana. When you get Shroud of Saints it's your saving grace. So nice. So just keep spamming that Cure , and remember it's okay if the tank isn't at full HP. Usually unless I'm preparing for big damage I keep the tank at around eighty percent.