This guide is meant to teach the basics of playing a level 80 rogue in PvP and PvE for patch 3.1.0 with a mutilate build.  Since it is generally accepted that, since the buffs to the assassination tree and mutilate since Burning Crusade, mutilate is one of the better specs for both PvE and PvP, this guide will cover that.

PvE:

For PvE'ing, you will generally want to use the build:
Build 1, Which is 51/13/7

A second variant of this is:
Build 2

Which gives you Vigor and Quick Recovery instead of Murder, which doesn't work against the undead mobs inside of Naxxramas.

For poisons, you will want to use instant poison on your main hand weapon and deadly poison on your off hand weapon. 

For weapons, you will want to use fast daggers, however a slow dagger *can* be better if it gives a large jump in stats.  The fast daggers mean that you will have more instant poison procs and focused energy procs.  This makes up for the lost DPS due to using faster daggers. 

For glyphs, there is a bit of an opening for a personal preference with major glyphs.  The recommended major glyphs are Rupture and Slice and Dice, leaving room for one more major glyph of your choice.  None of the minor glyphs are really necessary at all, so you are able to pick and choose here depending on what you think would help you the most. 

The glyphs are all situational, so you will want to think ahead to what you may need to do.  For example, if you are a rogue who likes to pick pocket as much as possible ahead of time to try and make some extra money off of raids, using glyph of pick pocket for extra range may be the best choice for you.  If you need to vanish often and run out of the pack, glyph of vanish would be the best choice for you.

The hit cap on rogues at level 80 is 752, assuming you have 5/5 precision (5% increased hit) in your build.  Without this, the hit cap is 919.  However, with 5/5 in precision as well,  315 hit rating means that your poisons will never be resisted, with 446 being the required hit rating without precision.  However, the hit cap here is unrealistic with the current gear in World of Warcraft, so it is recommended to try for the 315(446) hit rating cap for your poisons.  At 262 hit rating (99 with precision) you will never miss a yellow attack on a raid boss, so this will up your DPS where it counts in raids.

Other stats you will want to use for rogue PvE are: agility, expertise, haste and critical strike rating.  You will want a good balance of these four stats after your hit cap is reached, as to further increase your DPS.  Hit rating is a priority, however, as you do much less damage if you can't hit at all.

For your general rotation, you will want to do the following:

• Hunger of Blood stacked three times
• Garrotte
• Slice and Dice
• Mutilate to 5 combo points
• Envenom
• Mutilate to 5 combo points
• Rupture
• Mutilate to 5 combo points
• Envenom

…and continue so on and so forth.  Envenom will be resetting your slice and dice timer to its maximum, five second timer, due to having the cut to the chase talent.  This time is increased with the slice and dice glyph, giving you even more time to get your combo points built up.  If you are fighting a mob that is immune to poison for some reason or another, your rotation would be:

• Hunger of Blood stacked three times
• Garrotte
• Slice and Dice
• Mutilate to 5 combo points
• Rupture
• Mutilate to 3 combo points
• Slice and Dice
• Mutilate to 5 combo points
• Rupture

…and continue on with that rotation.   

PvP:

For PvP, the main build that is used is:
PvP Build which is 41/5/25.  There are many different variations on this build, which consist of a few points being moved around in the assassination tree.

For poisons, you will either want to use wound poison main hand and mind-numbing poison offhand, or use would poison on both weapons.  Both of these will cause crippling poison to be applied to your target due to the deadly brew talent, which frees up a poison slot for you to use.  Double wound poison is better when you need to do extra damage, but using both wound and mind-numbing poison is a better choice when going up against a caster, as mind-numbing gives you extra time to deal with their spell cast. For weapons, you will want to use two slow daggers.  Two slow daggers will give you much more burst, which is what PvP is all about.  The build linked here is also assuming you are using slow daggers.  Fast daggers will work for PvP, but they will be more for sustained DPS just like they are in PvE.

For glyphs, there is a lot of choice here as well, just like with the PvE glyphs.  These are based even more on play style, helping keep yourself alive and take down your opponent.  The only glyph that could be considered required here is glyph of vigour, as it gives you an extra 10 energy to use, allowing you to burn your target from the initial cheap shot for longer.  From there, the next glyph I would recommend is glyph of eviscerate, as it helps you burn down your opponent faster by allowing you to have a higher chance to your critical strike chance.  While not necessary, 10% critical strike chance to a finishing move you will be using very often will help you more often than not.  All glyphs, major and minor, have their own purposes, however. The hit cap for PvP is, as always, 5%.  Due to not having precision in this build, that means you will want to 79 hit rating, which isn't very tough to achieve.  If you do change to a build that has 5/5 precision, you will be at the PvP hit cap with just that talent and not have to worry about it.  Hit rating is much less important in PvP than it is in PvE, so you don't have to make it a top priority.

Other stats you will want for PvP are the same as PvE, with the addition of some stamina and resilience if you feel you need them.  So far with Wrath of the Lich King, rogues are able to PvP just as well as normal in PvE gear as they are in PvP gear.  This means the stats you should work on come down to a personal preference again.  You can either opt to burn down your target as fast as possible, while being very squishy, or decide to take a bit longer to take someone down in exchange for being able to survive longer. For your general rotation, you will want to do the following:

• Cheap shot
• Mutilate
• Kidney shot (when cheap shot is about to wear off)
• Mutilate to 4 or 5 combo points
• Rupture an armor heavy target, or Eviscerate a low armor target. 

This is a basic rotation, without using many cooldowns to lock down your target.  As there is no set rotation that you can use 100% of the time in PvP, I can only give you a general idea what to do.  Your opponent will more than likely have a trinket on him to get out of a kidney shot, meaning you either starting fighting him out of a stunlock or you can gouge him, or blind him, or vanish and cheap shot or garrotte again, etc.  The only other two rotations I can give you are very situational, as they are for against a mage. If you are feeling risky, and you need to keep the mage locked down so as to keep him from casting on someone, you can do the following: 

• Cheap shot
• Mutilate (assuming he hasn't blinked yet)
• Sprint
• run to the mage, and Mutilate if you didn't get to before you sprinted
• Kidney shot
• Mutilate to 5 combo points
• Cold Blood
• Eviscerate

This will do a lot of damage to the mage, while allowing you to try and keep them under control.  This can be stopped easy, however, by the mage either using frost nova to stop you, or getting a polymorph on you.  You may need to pop quite a few cooldowns in order to do this, so it is only really smart to do so if you MUST have the mage stopped.  Otherwise you will want to do this:

• Garrotte
• Mutilate
• Rupture or Eviscerate (can use cold blood on this eviscerate to add damage)

…and from there spam mutilate and eviscerate on there.  This is a much safer alternative to the above, but the mage will be able to start casting again after the short duration of the silence on garrotte wears off.