I've tried a number of classes, in a variety of content, and at the end of the day I really feel like I have a decent handle on the role of Healer. I use a high elf templar (CP310 - mix of Sanctuary and Sorrow gear), and have had a lot of success in dungeons with random groups using a main bar which allows me the following strategy:
I tend to follow close behind the tank and let him/her get set up, then drop Extended Ritual and Channeled Focus as close as possible.
Then I pull back to the perimeter and try to circle and watch where the DD players go, so they're all in range.
I finally figured out that BoL (my third skill on the bar) is not as good for sustained healing, but emergency situations where the whole group takes a huge hit. Now I use Rapid Regen (my fourth skill) to give people a little bump if they look like they're taking damage.
My fifth skill up until now has been the shards, which have worked great for their mix of damage and resources. However, I recently unlocked the Necrotic Orb and tried it a couple of times last night. It seems to serve a similar purpose, although I'm not sure about the mechanics of it moving across the battlefield. This seems to help it tick away more damage over a wider span, but I wasn't sure if it helps the team or not. Is there any advantage to me using one of these over the other, or is it situational?
My other bar has a lot of damage based skills like Elemental Blockade, Puncturing Strikes, and Radiant Oppression, but in truth I rarely swap to this bar. Seems like every time I start to offer some contribution to group damage, someone gets dead while I'm trying to swap back. I have been using the Shards as my damage contribution to healing.