Hey fellow healers of the galaxy far far away. I am writing this post because I want to see this site become active again, because...well...it should be. Reply, flame, whatever, just do something ;)
I'll try not to talk too much about one class or the other, all this info applies to both sages and sorcerers but the talent spec, some spell names etc may need to be looked up for the appropriate counter-class spell.
Here I will try to provide some of my experience and trial and error I have been doing over the last months to try and make myself as good as I can be.
For starters, here is the talent spec I use for both PvPing and doing HM's, it is good for both and I know there are many other specs that give more cc's, rooting etc etc but you simply don't need it. Going with this build you can utilize your longevity in fights to maximum potential. I am not talking about survive-ability because that is purely moot, think about yourself as a fly...stick with me here.
You are pretty much looking to be avoiding attention as much as possible, because as you most likely know, we are really keen when it comes to dying. When the warzone starts just hang back and don't be the first person into a brawl, if at all. Our job is to stay alive, so that we can keep our teammates alive, so that they can do the objectives, so that we can win :D
You cannot achieve this by being in the thick of it. Try to keep LoS (line of sight) with the enemy to a minimum, only breaking this to use a stun/interrupt or some other CC. If you want to do damage, respec. It's as simple as that, I know it's hard to admit it but we can no longer sit in the middle of a s**t storm healing through all damage like we were the Emperor or something o.0
I'm not going to go through tactics for each warzone because simply put, it would take me ages and I want to play at some point today. But I will lay out some logic and knowledge for you, Spock style. Firstly, Powertechs are mean (Vanguards for sorcerers). Avoid them as much as humanly possible because you will die either way. Secondly, if you get targeted, run! It's the easiest thing for us to do and we have all the tools to do it. Try and slow your attackers down as much as you can, stuns, slows, anything to get them away from you, then speed off like Road Runner to the nearest ally in the vicinity. If you get stunned, don't panic. Once again you have tools for such occasion. CC breaker in PvP is a crucial tool, you don't want to use it in a no-win situation because you don't want it on cooldown when you are running through a fire pit on Huttball and you get stunned right in the middle. But similarly, you don't want to save it forever because it's also very handy in a tight spot. You can never really plan the best time to use your CC breaker but with enough experience and observance you can generally tell when or not to pop it.
Going to leave it there for now, I will probably update this with more information as I check back. Hope it's not too much of a wall :)
tl;dr don't panic, run away, heal.