The current (4.0.6) recommended spec is 31/2/8 with the major talents in this build being:
Vile Poisons - This talent combined with the Assassination rogue talent Master Poisoner (see below) and their major Mastery Talent - Potent Poisons, this talent will help push an Assassination rogues poison damage to the top the breakdown list of damage sources for any given fight.
Master Poisoner - Increases poison (spell) damage to the poisoned target and more importantly stops Deadly Poison being consumed by Envenom, vital for increasing an Assassination rogues DPS as 5 stacks on Deadly Poison will always be on your main target ensuring hard hitting Envenoms
Venomous Wounds - The main reason an Assassination rogue should always keep Rupture up on their target. While the increased damage in nice the main selling point of this talent is the energy regeneration the talent can potentially give. Increased energy means more energy per 'fight' increasing the amount abilities can be used therefore increasing overall DPS.
Vendetta - Assassination’s 31 point talent. A good flat overall DPS increase, not a very inspiring or interesting talent overall. Activate Vendetta whenever it is off cooldown = increased DPS, that's it.
The current recommended Prime Glyph's for an Assassination rogue are:
Glyph of Mutilate - a no brainer, less energy required for Mutilate the more energy you have for other talents/abilities.
Glyph of Rupture - Increasing the time Rupture ticks for means more potential energy gains from Venomous Wounds and allows energy to be spent on other talents/abilites
Glyph of Backstab - Once your target reaches =<35% health Backstab will replace Mutilate as an Assassination rogues combo point generator (seel Rotation below). This glyph will help an Assassination rogue gain additional energy for other talents/abilities or for additional Backstab strikes.
The current recommended four Major Glyph's that an Assassination rogue can choose (three) from are:
Glyph of Tricks of the Trade - Removes the energy cost of your Tricks of the Trade. Tricks of the trade is a handy ability in any environment, whether it be giving a tank an aggro boost at the start of a fight or increasing the DPS of a fellow raid member it should always be on your bar/mapped to a hotkey.
Glyph of Feint - In the current Tier of raids in Cataclysm (Tier 11) you will be amazed at how often Feint should and will be used to not only save the healers some mana but save your life. By removing the energy cost of feint this greatly improves the opportunities you get to use Feint (it's still on the Global Cooldown) in any given situation.
Glyph of Fan of Knives - Increases the radius of Fan of Knives by 50%, handy for large trash packs and/or bosses with multiple adds that need to be DPS'ed down.
Glyph of Sprint - Increases your sprint speed increase by 30%. Handy, not optional.
You will always want to open from stealth such that you get as much of your 20 seconds of Overkill as possible. It is better to open a fight with Garrotte rather than Mutilate to maximise the energy returns from Venomous Wounds. Once in combat, there are various sequences of abilities that work but ultimately you will want to get Rupture and Slice n Dice both up as quickly as possible, 1 to 2 combo points is ok at the start.
100% to 35% target HP
The priority of finishers is as follows.
Slice n Dice > Rupture > Envenom
At this point, you will use Mutilate as your combo point generator and maximize your rupture uptime then maximize your Envenom uptime. To maximize your Envenom uptime, you should try to not overlap the Envenom buff when possible.
The best idea is to pool ~90 energy just before using Envenom such that when you Mutilate after, you have an increased chance to proc your poisons. Your rotation will be 1+ Rupture and 4+ Envenom; meaning if your Rupture is falling off, put whatever combo points you have into a new one otherwise do 4 or 5 combo point Envenoms.
35% or less target HP
Once your target reaches 35% HP, you will stop using Mutilate and instead use Backstab to generate combo points. You will still follow the same priority order and maximize your Rupture uptime and then Envenoms and pool before using Envenom. You will want to do 1+ Rupture and 5 Envenom instead.