The place to start with inter-player combat (PvP), in my opinion, is in a battleground (BG): Warsong Gulch, Alterac Valley, Arathi Basin, Eye of the Storm, Strand of the Ancients, and, for all practical purposes, Wintergrasp.
Dueling and arenas tend to involve experienced opponents in good PvP gear. It’s hard to learn from your mistakes when you are dead before you can do anything.