Welcome to my Necromancer PvP healer build!
This build is powered by a combination of Almalexia's Mercy, Braided Tether, and Spirit Healer. These give us a ton of passive healing, as long as we keep them up. Coupled with the resistances we get from Mark of the Pariah and Summoner's Armor, this gives us high survivability, allowing us to focus on healing our teammates.
Use the resto staff spells to keep your teammates alive, coupled with Resistant Flesh. Tag enemies with elemental drain as you can, for sustain and debuffing.
Agony Totem on the backbar is a flex spot. You can use that, or Unnerving Boneyard, for the debuff, or Blinding Flare, for Major Protection and steath detect.
A few words about the ultimates. Goliath gives you an emergency recovery option and is highly recommended. Colossus is great for when teams cluster together, but may not always have great utility. The healing staff ultimate is useful, but I prefer Goliath for emergencies. Reanimate can be useful, but the utility is limited by the narrow respawn window when you're playing Battlegrounds. It has more uses in IC and Cyrodiil, but I would still recommend Colossus.
The armor is designed to optimize survivability, but if you find sustain is too hard with four pieces of heavy armor, you can swap the Chokethorn to light, or some of the Pariah to weapons or jewelry and replace it with Almalexia pieces. Make sure to keep one piece of Pariah on your chest, for maximum benefit.
Finally, make sure you have fun!