Well sort of the point of my post was that I don't think I'm particularly good, but sure, I'll share some of my experiences (though priority list wise, I covered the basics in the OP).
First, for any sages leveling up in pvp (and anyone else for that matter), people should realize by now that buying bunches of the 42/46 weapons to use the expertise mods in orange gear is the way to go. I think I was around 5% from expertise from level 41 on, and it really makes a difference.
That aside, healing with a sage is really easy. Like I said before, keep your bubble up on yourself at all times and also on your friends as much as possible. If you are gonna focus heal someone and when you click his frame force shield is a valid option, it should be your first choice (unless maybe he's still near full and you'd rather get conveyance up for the cooldown to start I guess, but follow with bubble immediately).
Which brings me to the conveyance point. It's pretty much awesome and the central feature of your healing. If you've ever thought your HoT isn't that great so you don't use it much, just force yourself to accept that the point of it isn't the healing at all...its conveyance.
Next, I agree with Haeso, but didn't say it before because I wasn't actually sure...healing trance is personally my go to heal if it's not on CD. The reason I gave before stands...bad or slow interrupts means healing trance gets a good amount off before they affect you. Plus it's your mana regen. Following conveyance it's gonna crit, so net mana gain (just don't forget to use it).
Next, if HT is on cooldown, go ahead and use deliverance, but still try to get conveyance up first if at all possible. Otherwise the longer cast is just asking for an interrupt.
Last, for people who have the AoE heal, remember that if nothing else it's a good proactive heal. You're on a node and several baddies inc? Throw down your aoe right before they get to you and your friends.
----
If you're getting pressured as a healer, it means the other team has there stuff together. I'm not claiming I do any better than the next guy in such a scenario, but at least remember that if the other guys are fixated on you, you can often sprint away and keep them off objectives.