Let me say first that I'm not referencing some sort of vampire fetish, I'll leave that to our resident Twilight fan. I'm talking about riding around Azeroth, slinking in the shadows, preying on the weak and undefended. Ganking is a great stress reliever, it allows you to vent all of your frustrations and shed your rotations: there's nothing left but a pure kill. Coating your weapons in your opponent's vital fluids and having their warm blood splattered all over your armor is the perfect way to christen your new gear.
A rogue's ancient rite of passage, the art of the gank has been set aside by many for more important tasks. All work and no play will not only make you dull, but your weapons as well. As trained assassins, we are masters of destroying unsuspecting targets before they even realize what's happened. Death from the shadows, we disappear as if we've evaporated. Built from the ground up as killing machines, no other class is as feared in the open world. Once your opponent hears the 'whoosh' sound of stealth, they know their life has come to a tragic end.
Always snare the victim
There are a few keys to ensuring that your target doesn't escape your grasp once you've selected them for death. Crippling Poison is a must for enemies that will attempt to escape once you've engaged. A combat or subtlety rogue will be putting Crippling Poison on their off hand, while a Mutilate rogue will be able to use Instant Poison via Deadly Brew. Either way, slowing your target down is key to keeping them within your deadly range. You'll want to use Wound Poison on your other weapon, because if you allow a healer to get any casts off, the gank could turn around very quickly.
Targets trying to evade you will be one of your primary concerns while you're out on the killing field. Many of your weak opponents will see running as their only option. I try to save Sprint for situations in which the target is fleeing, as this will let you get back in range before they can get on their mount and fly off into the clouds. With Cataclysm's promise of bringing flight to the old world, your chance to stalk prey without fear of them escaping on a drake is quickly diminishing. The Lunar Festival is a great opportunity to stalk prey in Azeroth: a steady stream of enemy players will be making their rounds to visit all the Elders for their achievements. I also enjoy ganking in Wintergrasp, as many players will make the mistake of traveling away from their pack.
The tempo of the shadows
Think of a gank as an elegant dance with an unsuspecting opponent. You're the only one who knows the music, and so it's your duty to set the tempo. As opposed to our typical PvP strategy of reacting to our enemy's steps, we take the lead. Figure out your opening strategy, your plan for countering your opponent's abilities, and their possible escape routes. If you are anticipating their moves, you can proactively counter them before they even attack. By using your stuns and incapacitating abilities, you are able to pause and analyze your target properly.
Assuming that you open with Cheap Shot and follow up quickly with Kidney Shot, the victim will be mashing one of their powerful abilities Paladins will typically use a Hammer of Justice on you immediately after being freed from your stuns, priests usually prefer a Psychic Scream. Preemptively using Cloak of Shadows as your stun duration wears off makes them waste one of their most powerful abilities and saves your PvP trinket for a more crucial moment.
Stealth and surprise
The element of surprise allows us to survey the battlefield and choose our time to strike. It's truly our class-defining ability, especially in an open world PvP situation. We can wait until our opponent is distracted, weakened, or in opportune position for our strike. Many players aren't quick on their feet, and you can destroy them before they're aware of what's happening and able to respond. Enter the shadows before you're spotted, take your time working your way up to your prey, and ensure that they're not aware of you before you engage.
Without stealth, nearly any enemy will have a chance to mount up and evade you, which can actually just be wasting their own time. As seen on several PvP videos (and easily testable), combat rogues can use Killing Spree to kill airborne targets. You'll need some way to survive the fall, an engineer can use the Parachute Cloak and everyone else can make use of Noggenfogger Elixirs. However, it Is more important to never let your targets leave combat so that mounting isn't an option. Make use of Deadly Throw, regular Throw, and any other ranged goodies you may have access to in order to keep them in combat for as long as possible.
Ganking is also one of the very few environments where a subtlety rogue can thrive. Shadowstep is an amazing tool for ambushing your target quickly and also preventing their escape attempts. Two sets of cooldowns via Preparation and significant Stealth improvement talents bolster your ability to remain undetected on approach and handle situations where you lose control. Remember, style kills are worth two points, so feel free to Gouge that low HP mage, run back a few steps to toy with their hope, and finish them off with grace using a Shadowstep->Eviscerate combo to tear apart their insides.
No holds barred
Rogues play dirty, and that's all there is to it. Pop all of your cooldowns when you're picking off an opponent: you won't need them once your target is dead. Killing Spree and Cold Blood provide some powerful on-demand burst that work well with the quick paced tempo of ganking. Don't hesitate to use every tool in your kit, use Blind if the situation is going poorly or Vanish if you've bitten off more than you can chew. There's no honor in dying to a prot paladin who you misidentified as a squishy target, get out of there and try your luck elsewhere.
After a romp in your prey's eviscerated entrails, relish in the kill. You're venting your excess stress, you're getting a chance to experiment with new weapons and gear, and you're energizing world PvP all at one time. Without a mutual fear and hatred between the Horde and the Alliance, the war will simple fizzle into giving each other the cold shoulder. Blizzard intends to rekindle the bloodbath between Azeroth's factions, so get some practice in while your opponents are soft so that you're ready when they're battle-hardened and ready to strike. Don't neglect to kill lower-level players either, drilling a healthy respect for the opposing faction into them early will make them more likely to PvP when they're fully grown.