Although going full on into the Assassination tree is primarily considered a PvP talent build, this guide will focus on ways to maximize your DPS while in PvE using Assassination.
The Strategy
It would be semi-unnatural to go into the deep end of the Assassination tree and not use mutilate as your primary attack unless you are using a Seal Fate Hybrid Build. If you are going to be using this build then your primary opener is going to be ambush for dps, followed by spam backstabs. Your combo point regeneration will be fairly fast so be prepared to use Eviscerate or Rupture frequently as your finishing moves.
Typically you will use eviscerate if the mob is at low health and Rupture if there is still time left to get the full effect of the Damage over Time.
The build most people will use will be a Mutilate Build.
This build will require the use of dual daggers and you're main attack from stealth can be a variety of things depending on the situation. There is a substantial damage bonus given when using mutilate to poisoned targets so you will want to use a poison that will stick to your target, whether it be crippling poison or deadly poison. You can put this on your offhand if you feel comfortable with it's proc rate, if not then go ahead and put it on your main hand.
If you are soloing your opening move will probably be a cheap shot to stun the target and apply a poison so you can follow up with a mutilate (requires you to be behind the target). After that you can land a kidney shot and/or gouge to get back behind the target again for another mutilate.
Keep in mind that if your target isn't poisoned when using mutilate that you may be able to obtain more damage by using backstab instead.
For raiding or grouping you will notice that we went into the combat tree and grabbed imp slice and dice, precision, and dual wield. This will substantially increase your white damage output. Keep Slice and Dice active and keep spamming mutilates.
The Talents
If you are using the mutilate build above there is room to move around some of the talents.
Exposed armor isn't necessary for most groups because there's a good chance you'll have a warrior that is doing sundering armor on the targets, you can move these points into lethality.
Also Vile poisons will increase your damage output from poison but if you're finding yourself not getting poison applied to your target before you are ready to mutilate then try moving these points into Improved Poisons or finish off Lethality.
If you are using the seal fate / subtlety hybrid build you can also move around the same things in the assassination tree. For the Subtlety portion of the tree you could move Master of Deception into Camouflage if you like to move around in stealth faster. You also get Improved Ambush that you can open up with which will most of the time put you at 3 combo points if it crits. This build focuses on very high combo point regeneration so I hope you can get rid of your combo points fast enough.
These are probably not the highest DPS builds but the tips above will help you maximize your dps if you still wish to spec into this tree. Thanks for reading.