World PvP
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If any class had the ability to grief someone in World PvP it is definately the rogue. A rogue can sneak up on anyone unexpectantly in World PvP and ruin timed quests, corpse camp them, wait until they are PvE'ing and then jump them, one shot them at low health, and all sorts of ways you can piss someone off in World PvP. The strategy is pretty simple since most of the time as a rogue you will be initiating the fight. You can gear up your poisons to the class you are going to jump (I rarely need poisons in World PvP) and then you can either go for cheap shot or an ambush as opening moves depending on your gear and just whack away. If you have a lot of time on your hands wait until they are fighting before you jump them again (it really pisses people off). In the event that you are not the one initiating the fight in World PvP be prepared to use your evasiveness, blind, vanish, and other rogue abilities because they are most likely needed. Hunters have a bad habit of getting rogues marked, snared, or dotted but if you are quick enough and have shadowstep you can be a hunter's worse nightmare especially if you have a crippling poison active. I have my hotkeys set for skills like Vanish so for me to get a hunter all I do Vanish, Shadowstep, Ambush and watch him cry. You can hit all those keys in < 1 second before any dot or shots take off your stealth. World PvP can be super fun and spontaneous, it's by far the best PvP mode for rogues.
Battleground PvP
Battleground PvP for Shadowstepping Ambush rogues is just like farming honor. What I do is sit stealth during big battles, toggle targets to find one low health, shadowstep / ambush, then walk out of combat and do it again. I almost always lead killing blows on my server for all battlegrounds. If you want more honor per kill then wait away from the raid to where people with low health usually escape to or are least expecting it. Typically you want to avoid fighting warriors who wear a shield or paladins with decent gear. It's not that they are good, it's that they won't die, and by the time you finally kill them chances are you have wasted 30 minutes of your life or some of his buddies have come along to help them out. It's not worth your time. So many n00bs play the Paladin class and think they are good at PvP that it makes me cry. Avoid them at all costs if you can in 1v1 situations unless you know you are far more superior geared or can get enough stuns in to stop their gayness; it may end up costing you 30 minutes of your life that you can't get back. Look for cloth wearers or those with low hp and just wail away.
Dueling
Dueling is probably where the rogue has the greatest disadvantage but it depends on the skill of your opponent. The biggest advantage of the rogue in PvP is choosing when to start the fight and who to fight, in duels each person can prepare for the battle. "Hold on let me get my poisons on and bandage myself" <--- How lame is that. Most of the fights are scripted by what class you are fighting and even by what gear / weapon setup they have on because in duels you have time to inspect or determine all of that. "Okay I'm fighting a shadowpriest let me put on my poisons to slow his casting time and then I'm going to start in stealth go in for a cheap shot and try to stunlock him. If the stun comes off I'm going to be feared that's where I pop my anti-fear item of my choice and go back in for a gouge or perhaps vanish and cheap shot again" Yeah that sounds like fun. All you n00bs that duel with your rogue and think you own, get a life. You might as well go play RTS if you want to strategize and scout out your opponent.