I'm new to MMO's, but I've played maybe 200 WZs with a DPS spec, and recently switched to healing. Here's what I've learned as a healer:
1. Tank-Healer combinations are very powerful. Use Guard.
When you (The Tank) takes damage if gets reduced. When I take damage it goes straight to my face. It's more efficient for you to take the damage and then me heal it.
If you are a tank, find a healer and put them on Guard. Talk to them before the WZ starts and coordinate with your healer. A weird part of the UI is that I can't tell who is Guarding me, so let's talk.
I will follow you like a puppy keeping you alive and un-interrupted.
Healers without tanks are not nearly as efficient.
2. All I want to do is keep you alive.
Honestly, it's hard for me to keep up with objectives on the map, it's hard for me to deal much damage. I spend about 90% of my time looking at your health bar. I need you to stay goal oriented, I'll try to get you there.
And for f's sake don't throw me the huttball. Throw it to my tank.
3. I work best in groups.
I can generally keep 3 or 4 of you alive at any time. If I'm alone I die. I need to follow a couple of you around. Coincidentally, generally attacks go better in groups, so group up. I'll get your back.
4. Give me some props.
I earn way less medals than I'd do if I was DPS. That's cool, and I don't mind not getting MVP votes or anything like that. But once in a while say 'thanks for the heals'. It seems simple, but that really keeps me going. I'll be sure to thank you for the Tanking.
I usually don't have the luxury of a tank following me around, and I do really well with healing in some groups and I have a miserable time in others.
This is due to the fact that some DPS on my team just will NOT get enemy DPS off of me, then I start having to heal myself, my teammates die while I can usually get away, but whatever we were trying to accomplish has then been lost.
I mean, is it really that hard to watch out for the person healing you and get the 3 melee DPS off of the healer?