Basically you just run around, try to keep your distance. Just attack with your staff and heal yourself, your allies and if needed you have mobilty with the flash and the vampire stealty passive. But since many enemies will charge you, you just surprise then with vampire ult just before you die. I like to be stage 4 because of the stealth btw. You don't need the health regen but you need the reduced cost on your ult.
If you don't have scribing, just use crystal weapons from dark magic skill line.
This build will not make you unkillable. It will give you a good and relaxing start in the pvp world.
It is modified to function better in a group. You are like an off tank. Get the attention away from your team mates. On BG it also helps to just run in stealth to the backline of the enemy team at the start of the game. You can distract the enemy and focus the healer first.