With dual spec, you have no excuse to not have 2 sets of gear. I swap out about 10 pcs of gear between PvE and PvP (helm, trink, chest, legs, bracers, boots, weapon, neck, belt, ring). With 20 slot bags so easily attainable, you should be able to carry an extra set in your bags without a problem. I currently use a simple /equip macro to single click switch between sets, but soon enough Bliz will implement a gear set app to make things even easier.
Heres an amateur synopsis of what you need to do (assuming mutilate build for both).
PVE - Get to the poison hit cap, or close. ~315 +hit, unless you've got a player in your group that gives you the 5% spell hit inc. Then the numbers around 267 (I think). Expertise is important, there are weights you can find on EJ or in this forum that shows the importance of each stat before and after hit cap is reached. Exp. cap is 26 or so, but alot of rogues go for 22-24 exp. AGI AP are still important, +crit is less so as your raid buffs should be sufficient in that department. If your hit isn't high enough, look for Icewalker on boots (cheap), +20 hit to gloves and bracers, and the yellow +16 hit gems (rigid I think). Titanium weapon chains are cheap and give hit and crit (I think) if you don't have the $ for Beserking, or your weapon isn't good enough to warrant an expensive EC.
PVP - For starters, don't gem for Stam or Resil. The gear you can get from either a.) Honor farming or b.)raping OS or Vault should have plenty of resilience to carry you to the arena, if that's your destination. After that, you'd need to give some specific goals (world pvp, high end arena, bgs..etc).