1. Come prepared. Yeah, showing up at the right place at the right time is a big part of raiding, but there's a lot more to being ready to raid than just being physically present. First of all, read up on the strategy for the boss you're facing. Asking "What does this boss do?", or worse, not asking and wiping the raid, is a good way to ensure you'll never be back in that instance. Take five minutes before the raid and check out Bosskillers or WoWWiki.
Another aspect of coming prepared is bringing consumables. For rogues, this means poisons/sharpening stones, battle elixirs, and healing potions at a minimum. You want to always keep a stack of Instant Poison, Deadly Poison, and Anesthetic Poison on you at all times, and I also bring all the other poisons in case the enemies are vulnerable to them. Good battle elixirs include Fel Strength Elixir, Onslaught Elixir and Elixir of Major Agility. I also bring Elixir of Major Fortitude, Insane Strength Potion and Haste Potion.
Your raid will also want you to download certain mods. Some form of boss mod and threatmeter is pretty much essential to fights nowadays -- I use Deadly and KTM, respectively, but there are many choices. Damage meters can be good if you want to compare your performance to other rogues, but can become the bane of raid groups if you get the "I'm topping the damage meters! I'm topping the damage meters!" attitude. There are a number of rogue-specific addons as well. Three worth mentioning are Slicer, which provides a visual timer for your Slice and Dice, PoisonPouch, which makes buying and applying poisons easy, and StunWatch, which can help you time your stuns on trash.
And finally, make sure you're personally prepared for the raid. Eat if you're hungry, drink if you're thirsty, finish your work or homework, close the naked picture website. I like to concentrate on the raid (and alt-tab out during breaks to read forums) -- however, the top rogue in my guild raids on speed and techno music and does great. Whatever enables you to have fun and do your best.
2. Get a decent raiding spec. "Decent raiding specs" include combat swords/fists/maces, combat daggers, and (against non-poison-immune bosses) mutilate. Generally, anything deep in the subtlety tree is not going to be great for raiding, although there are still some diehard hemo spec players. Combat is best for sustained DPS, as it benefits the most from gear upgrades and can also function as a pretty good PVP spec. Mutilate can work well if you have the gear for it, as mutilate crits can be sky-high, but the spec hits the dust when the boss is immune to poison.
Currently, combat swords is considered to be the build with the maximum potential DPS, but the combat swords playstyle isn't for everyone. I'm 15-41-5 combat daggers using the spec above, and I love my sustained damage, energy regen, and ability to hit Adrenaline Rush and Blade Flurry for those all-out-burn-down fights. If you have a spec idea, feel free to post it on the rogue forums and ask them for comments.
3. Know that you can do more than just damage. Specifically, you can stun, interrupt and poison. Stuns are invaluable when fighting hard-hitting trash mobs. Stunning trash can help keep your healers' mana up and your tanks alive. However, most tanks want to get a couple whacks in on the mob before you Cheap Shot it, unless you are utterly confident that you can either burn it down before it gets out of stunlock or tank it yourself. But if you have, say, an undergeared tank getting smacked for one-fourth of his health each time by a Kara mob, you might just want to step in and save the day. Stunlocking is easiest with a mutilate build, but even combat types can help out with the stuns if you have enough combo points at an opportune moment.
Interrupting spells is another important part of a rogue's job. A lot of trash mobs and even a few bosses (Shade of Aran, Magtheridon's channelers) have spells that need to be interrupted. Know when you're facing one of these mobs and put Kick on an easily-accessible hotkey. Many of these mobs cast spells quicker than your Kick cooldown will be up, so discuss who's going to stop what spells with your local other rogue/warrior/shaman. You don't want to kick a shadowbolt and then be caught with your pants down when the mob decides it's time to heal.
Poisons ... well, poisons serve many functions for a rogue. Instant Poison and Anesthetic Poison do direct damage. The latter should be used on aggro-sensitive fights, since its damage doesn't cause threat. Deadly Poison causes damage over time and stacks up to 5 times, and can be a nice way to keep dealing damage during any phase where you can't directly attack the mob. Crippling Poison slows the mob, which is excellent in PVP but doesn't often come in handy on boss fights. Mind-numbing Poison, which can slow the enemy's casting time by 60 percent, and Wound Poison, which can do damage and reduce healing effects on the enemy, are both excellent in certain situations -- however, most bosses are immune to these poisons. When they're not, though, the poisons do a great job. The channelers on Magtheridon are good examples of where to use these poisons.
4. Know where to be. You want to be behind your opponent at all times. If you're doing your damage through Backstab and Mutilate, the reason's pretty clear -- you can't use these abilities from the front. But even if you're swords, maces or fists, you should be behind the mob for a couple of reasons. First off, a lot of bosses cleave these days, and cleaves tend to be 180 degrees in front of the mob. Staying in the back will keep you from getting one-shotted by a nasty cleave. Secondly, mobs can parry attacks made from the front, but not from behind, so positioning yourself at the rear will increase your white damage. And finally, on most fights, it's easier for all the melee to stay together. That way, you can get chain healed and holy novaed, and if you notice all the other melee running away, it's a good sign that you should run away too.
Speaking of running away, most boss fights require some of that these days. The time of Ebonroc and Ragnaros is long past, and your bosses are likely to run around, AOE, or knock you into walls. Your boss mods should tell you when the boss is set to use certain abilities, so make sure which abilities require you to run (whirlwinds!), which require you to avoid other people (shatter!) and which require you to not move or your raid leader will hunt you down and kill you (flame wreath!)
5. Figure out the right finishing moves. You're going to be using Sinister Strike/Backstab/Mutilate most of the time, but there's still the question of what to do with your combo points. Out in the wilds of Azeroth, you probably spent them on Kidney Shots or Eviscerates, neither of which is ideal in a raiding environment. The most important thing for finishing moves is to always have Slice and Dice up. By increasing your attack speed, it increases your white damage and adds more to your DPS than any other finishing move. Each raiding spec -- combat swords/maces/fists, combat daggers, and mutilate -- has its own finisher rotations. The consensus seems to be:
Combat swords: 2pt Slice and Dice, 5 pt Rupture, repeat. If you have the two-piece Tier 4 bonus, do 1 pt Snd/5 pt Rupture. (In general, Rupture does more damage than Eviscerate.)
Combat daggers: 3 pt Slice and Dice, 5 pt Slice and Dice, 5 pt Rupture, repeat.
Mutilate: Depends, since the combo point generation is so much faster than combat. Always keep up Slice and Dice. If you have Vile Poisons and a stack of 5 Deadly Poisons on the target, Envenom can do quite a bit of damage since it ignores armor, although this is still up for debate. Spearmint of Gilneas suggests "Garrote, Mutilate, SnD if it was a crit, Mutilate again then SnD if it wasnt, Mutilate, Rupture if I'm at 4 points (probably not), Mutilate again then Rupture if not. Rinse and repeat." Mutilating again when you're at four combo points is a waste of one or two combo points.
6. Above all, learn. Learn from your class leader. Learn from the other rogues in your guild. Learn from rogues in rival guilds. Learn from the Armory. Learn from the forums. Learn from Shadowpanther's gear chart. If your DPS is lacking, ask what you can do to improve before someone tells you you need to improve. If someone does tell you you need to improve, listen to what they say.
What other advice would you give to raiding rogues?