Immediately when you step into ICC, you'll find the new T10 gear vendors. Feel free to drool over the new set, and then move on to taking out the trash between yourself and the first boss. Most of it is pretty standard stuff, although there is one specific rogue-only tip I can provide. There are a pair of traps in each of the starting rooms, that are visible while you are stealthed and can be disarmed. These traps will trigger a frost/slowing aura on your raid and will summon a giant skeleton add to come attack your group if they are triggered.
While you can safely disarm them from 20y away while in Stealth, remember that by skipping the mobs, you will lose out on 75 reputation with the Ashen Verdict for each one you skip. For this reason, I suggest you simply mark the trap with a flare or other notification, so that you can trigger it on your own. This will net you some extra reputation, which can be key as you work your way up the food chain towards the very awesome Ashen Verdict exalted rings. Once exalted, and on farm runs later, your raid leader will probably ask for these traps to be disarmed instead of activated.
First Encounter: Lord Marrowgar
The first boss of ICC is a giant flying triple-headed skeleton, and is honestly one of the most amazing bosses I've ever fought from a visual perspective. As a rogue, you are going to spend 99% of this fight burning the boss down. Ranged DPS will be assigned to popping the Bone Spike Graveyards that come up, and they'll be dodging the Coldflame trails that radiate out from the boss. Melee doesn't really have anything to worry about, as long as you remain a safe distance from the tank so you don't get cleaved by his Saber Lash attack. You might get put into a Bone Spike Graveyard (and no, Cloak / Vanish / Killing Spree won't save you), but you simply have to wait for your friends to break you out.
The boss will initiate a spinning whirlwind attack, similar to Skadi in Utgarde Pinnacle, though dealing significantly less damage. You can Feint if you are close to the boss to lower the AoE damage, but just running away will probably be fine. Be sure to avoid the fire during this phase, and also remember to Tricks of the Trade to your tank as his whirlwind is ending. He resets threat during this time, so your tank will need some extra help picking the boss back up. Because this boss is intended to be easily killed for the weekly raid quest, you won't really find too much of a challenge taking him out.
Second Encounter: Lady Deathwhisper
Here's a fight where a well-played rogue can really clean up a fight and make it easier for everyone involved. It plays out in basically two phases: mana shield up, and mana shield down. The 'mana shield up' phase is basically Freya from Ulduar, with the exception that you do need a couple of your DPS sticking on the boss at all times. As a Mutilate rogue, you should really ask to be left on the boss, as your mix of physical/magical damage makes you a bad candidate for taking out the resistant mobs. Your rotation also thrives in a single-target burn situation, and so you should try to get out of add killing duties.
As Combat rogue, you are well suited to handle some of the add control. There are two types of adds: Adherents and Fanatics. Adherents can gain near immunity to magic, while Fanatics can boost their defenses to be almost immune to physical damage. This means that you'll be focusing on killing Adherents, while your casters knock out the Fanatics. You'll want to kick as many of the Adherents' spells as you can, and use your CDs to burst through their Shroud of the Occult damage shield. Using Tricks of the Trade to help your tanks pick up aggro will also help with some of the tricky parts of this fight as well.
Once the boss' mana shield is down, due to the damage of the people on her full time, you'll want to switch to attacking the boss. Her key ability here will be Frostbolt, as it deals massive damage but can easily be interrupted with a Kick. Try to always have some energy in your pool to Kick this spell to save your tank some significant damage. You may get chased by a Vengeful Shade (one of those invulnerable ghosts), just run away!
Third Encounter: Gunship
The Gunship Encounter is one of the easiest (and most entertaining) raid fights I've had the pleasure of conquering. Pick up a Rocket Shirt from the engineer on-board your ship, and get ready to fight the opposing faction's Gunship. I find that rogues are best delegated to add duty on this fight, as Tricks of the Trade and their melee nature make them perfect candidates. Adds will spawn via a portal on your ship, assist your tank in killing these adds swiftly. Use Tricks and your other available tools to keep them at a minimum level. If you do get asked to visit the other ship, you simply use your Rocket Shirt to hop over and destroy the Battle-Mage that is freezing your guns. Killing Spree or Overkill would be utilized perfectly for this bursty phase, simply remember to jump back once you're finished!
Fourth Encounter: Deathbringer Saurfang
Saurfang rounds out the first wing of ICC, and his difficulty is definitely a step up from any of the prior 3 fights. He functions on something similar to a Runic Power / Rage / Energy system, where he builds up a primary resource, and then empties it once his tank is full. Your goal is to minimize how fast that tank fills up, while burning him quickly due to his soft enrage timers. The rule of thumb is that every damaging ability he uses will generate 1 energy for him.
The most prevalent mechanic on this fight is Saurfang's Mark of the Fallen Champion. Once Saurfang reaches 100 energy, he'll unleash this via a short cast on a raid member. Once cast, his attacks start hitting that target for a few extra thousand damage on every swing. This damage causes him to build up energy even faster, and he'll cast another mark, which eventually escalates into chaos. He also heals back up 5% of his HP if someone with the Mark dies, which means that the entire fight starts slowly and ramps up quickly. Save your CDs for the late-fight, as he has a Frenzy move that means you'll want to end the fight ASAP.
Rogues have a unique way to deal with this issue: Vanish. If a rogue uses Vanish to avoid Mark of the Fallen Champion, they can avoid having the ability cast at all. Note that if you Vanish too early, he'll simply cast it on someone else. But if you time it just right, you can Vanish/Immune the ability, effectively resetting his energy to 0 and yet not ramping up the pace of the fight at all. It's a trick maneuver to pull off, but there's no real reason not to blow a nearly-useless Vanish cooldown to switch this fight from difficult to cake. If you manage to be hit by the Mark anyway, reports are indicating that Feint will reduce the damage you take from the Mark. Doing so may or may not be worth using, depending on your healing situation. For further research on this, feel free to read the Elitist Jerk's thread on ICC rogue optimization.
His second core ability is summoning a few Blood Beasts which will then start chasing after your healers and ranged DPS. You can use Tricks to help one of your ranged classes gain aggro, or some raids may have melee pile onto one of the adds to burn it up. Whatever you do, be sure to NOT be hit by this add. Use Evasion, Kidney Shot, Vanish, anything that will save you from being hit. If you are hit, it starts feeding into Saurfang's energy timer, increasing the tempo faster than it should be. Don't bother using AoE on these adds, as they have the same passive aura as the Faction Champion that makes them super-resistant to it.
The first few bosses of ICC will give you plenty to practice on, especially if you're planning to tackle hard modes in the months to come. Luckily, there is still plenty of time for you to go back and work on ToC and Ulduar for achievements and gear, as we won't see any new encounters for another 3 weeks. Please share any other ICC tips you have in the comments, or ask any encounter-specific questions you may have.