Thana, one of the top healers on the Chaos data center across many seasons, has just put out an exceptional, in-depth guide to PvP healing. This guide is relevant as of Patch 4.06, and covers just about everything there is to know about playing the healer role.
In his guide, Thana doesn't just go over the fundamentals, such as UI layout and which extra actions and traits to choose. He also goes over specific Job knowledge, tips on positioning and pre planning, and even touches on how to approach healing as a new player. To top it all off, he explains the mindset that you need to have when healing, particularly in ranked solo queue Feast 4v4.
This really is one hell of a guide, and just about any player, not just healers, will be sure to learn invaluable information by giving it a watch.