Have you captured anyone's Elder Scroll? What kind of changes to your build did you have to make? A friend of mine uses different add-ons for his PvP character.
Capturing an Elder Scroll is way above a solo players abilities. It takes a big team of skilled players to nab one.
I had to completely re-do Haa-Rei's build. All his attributes, skills, champion points. He's now a stamina build, and relies on critical hits/critical damage and various buffs to keep him alive. Spent ages mooching about the ESO forums to see what abilities other players were using.
Cyrodiil is crazy unbalanced though. Some players are going around doing 20k damage with a single attack, and Haa-Rei only has 20k health.

He's a sorcerer and an archer, so we can't just dive into big fights. We spend a lot of time in stealth mode, scouting around, and fighting from the relative safety of high castle walls.
That is how that vampire's spell was that hit Misa - and it paralyzed her, she couldn't run away or fight back. Really powerful spell. I have no idea what class of spell that would be or if it was his vampiric powers.
But yeah, if you learn any tips or hints, feel free to post them here at Chorrol in case anyone here wants to try PvP. I have wanted to join the Alliance wars in Cyrodiil further on down the road, just not till I've done everything else in Cyrodiil and maybe after I've beaten the main quest or something.