World PvP, unfortunately, is never fair, and if you want to succeed in it, you have to follow the cunning tactics and be ready to forget about honorable combat, at least in some situations. The elixir of winning consists of a mixture of combat tactics, proper scouting, knowing strengths and weaknesses of your enemies, correct handling of negotiations and public relations and, most important, proper decision-making.
In nearly all cases except personal liquidations or vendettas, when more than 2 players of each side are involved, the group with bigger numbers usually wins, unless massively outgeared or outbalanced by presence of more healers, etc. In other words – if you got considerably more men, you will probably crush the enemy party.
However, not every situation is similar; very often there are other factors that can play along with either you or your opponents, such as: nearby city / village / strongpoint, a high cliff or a building, a cave, etc. Sometimes there are also friendly or enemy NPC, which can be significant enough up to turning up the tide in combat. You absolutely have to consider these NPC while defending and especially while attacking, even if you do have the superior force.
This was the introduction; now, let’s get to the details.
1. Getting equipped properly: items, gadgets, consumables and addons that make the difference.
1.1. Here is a small list of items that, IMHO, every serious World PvPer has to have in order to be maximally potent in present times (Mists of Pandaria):
*Hardened Shell: http://www.wowhead.com/item=86584
Dropped by rare spawn Nessos the Oracle in northern Kun-Lai Summit
The major must-have item in your inventory, this turtle shell can dismount an enemy player in flight if thrown from close enough range; the cooldown is 15 minutes, but the shell always hits.
*Crystal of Insanity: http://www.wowhead.com/item=86569
Dropped by rare spawn Sulik’shor in quest area of Valley of the FourWinds.
This item acts like a flask, except its effect wears off when you get killed. However, the cooldown is just 15 minutes, so you can use it pretty often. What is especially great in it, it gives you +500 to all stats, including Stamina, which boosts your survival in World PvP.
*Salyin Battle Banner: http://www.wowhead.com/item=86583
Dropped by rare spawn Salyin Warscout along the river in Valley of the Four Winds.
This item gives any non-stealth class an ability similar to Feign Death, which also gets you out of combat and removes you from enemy’s target. Thus, you can escape corpse camping or just get out of fight when you need it.
*Eternal Warrior’s Sigil: http://ptr.wowhead.com/item=86578
Dropped by rare spawn Gar’lok in Dread Wastes.
While usable only in Pandaria, this item can still be a difference between life and death, if you can get far enough from your enemy and use it.
*Overgrown Lilypad: http://ptr.wowhead.com/item=86580
Dropped by rare spawn Sele’na in Valley of the Four Winds
Grants you a Symbiosis ability as if a Druid cast it on you. Very useful, though can sadly be used only in Pandaria.