Never go into battle unprepared. Before you queue up for a Battleground or Arena, make sure to repair your equipment so it doesn't break in the middle of an encounter. PvP takes its toll on your armor just like in PvE, albeit at a slower rate, so always be mindful of your repairs. While you don't receive durability damage when you die, your equipment still suffers every time you get hit. I once PvP'd for almost 15 hours straight without repairing and had my armor almost break on me. Though far from being as expensive, PvP is an endeavor that entails costs just like raiding or other instances.
Always have a mental checklist for buffs when entering an Arena or Battleground; before a match begins, players receive a buff called Arena Preparation or Preparation which reduces the cost of all spells and abilities by 100%. This period allows you to buff yourself and, ideally, your entire team as well. Note that although the spells are free, they still consume reagents in Battlegrounds (but not Arenas) so be mindful of your stocks. It's always good practice to have full stacks of reagents, so remember to replenish now and again between battles. If you're a Mage or Warlock, your teammates will be extremely grateful if you throw up a Ritual of Refreshment or Ritual of Souls. Extend courtesy to your fellow players and be sure not to take more than Conjured Manna Biscuits than you actually need!
In Battlegrounds, dying is a good opportunity to refresh oneself for the fight. When running low on health and/or mana, don't rule out the option of dying to top yourself up, specially if there's a nearby Graveyard under your faction's control. Right after you rezz, you receive a 6-second buff called Spirit Heal, which reduces the cost of all spells by 100%. Considering global cooldowns, you can cast maybe up to three buffs for free before heading back into the fray. Remember to cast your most expensive buff first, and stack as many self-buffs as you can to provide a buffer for dispel abilities. Preparation pays off, or in this case, costs nothing!
Battle Bites is a short feature that gives out weekly tips for PvP. Have fun storming the castle!