A couple of things to keep in mind while healing in PvP. I'm not the best ever, but I'd like to think I'm above average.
1) Don't focus just on your raid frame.
-Be aware of what's going on. Just healing in a wz will not help you win. Use your stuns/mezzes/other utilities to help your team win. Big numbers are cool, but they are not the only thing that wins wzs.
2) Pillar humping!
-This is the most basic, yet underused tactic in the healer's book. LoS! LoS! LoS!
3) Know your enemy.
-When someone attacks you in a wz, know what they do and what to do to counter it. Go to Dromand Kaas or whatever the pub counterpart is off of fleet and duel people. You will learn what to expect and when. A healer is not expected to kill others, but to survive long enough for help to arrive (I know this really doesn't happen in regs). While you are kiting, you can spam some heals to your teammates or draw them off the node for a cap or whatever the situation demands.
Hope this helps some.