Just started PVPing on my arms warrior and if possible since I know here are people which have more experience to share some WeakAuras Strings or advise some useful Addons for PVP.
For PvP I'd imagine you want to track CDs duration/cooldown, certain dots you can counteract and whatnot. I'm not much of a PvPer, so I just use my PvE strings for it.
You can find my PvE strings here.
Another addon I like for PvP is GladiatorLoSSA. It simply tells you what your opponent is doing. Very neat. Just be sure to alter the settings so it announces your target and focus target only, or else you'll be spammed beyond belief..