Nightblade talent calculator, you can find bellow, will help you find the best build to match your playstyle as this, mostly, DPS class. Nightblade is the only class that has a vanish skill that lets you get out of sticky situation or prepare your most devastating attacks. Assassination Nightblades will be all about dealing damage (or buffing themselves to do the most damage). Shadow is the skill line you want to follow if you want to get utility abilities that will make you vanish and do the most damage while surprising your enemies. Siphoning is more about DOTs and leaching health. Great for weakening mobs while staying alive. Whether you use a bow, daggers or other means of dealing damage to your enemies, Nightblade’s skill will help you dispose of them the fastest. Pick and choose skills bellow and save them so others can see your preferred playstyle.
Dual wield stealth Nblade low lvl PvE
UPDATED: Added more passives and an ultimate. This is a good solo PvE build for up to lvl 30. Rotation stays the same and you can now pick another ability for 5th slot. Since I rely heavily on skills I am more concerned about having enough magicka and health for survivability than stamina. What you really want to go for is Executioner passive in Assassination and use Killer's Blade to kill all your enemies. This bumps back both your hp and mp. Down side of this whole build is lower weapon damage so without skills you are just waiting for your Magicka to regen. This makes it hard to take on more than one group of mobs. You also can have trouble with heavy armor mobs, but this is the downside of any nightblade build I guess.
After several tries I think I found a very nice Nightblade build for lower level PvE leveling. This build made it possible for me to kill single targets very quickly with low chance of dying. I can take on two mobs as well due to having a long range stun in the build.
During the tutorial section on Coldharbor I go for Shadow Cloak (which is your 2.5 second invisibility) so I can level Shadow skill line from the start. I also choose Assassin's Blade from Assassination skill tree as a finishing move to complement just my weapon damage.
As soon as you get enough skill points and Shadow level (either through getting skyshards or leveling) I go for Veiled Strike. This makes my rotation Shadow Cloak (when close to mob so I can perhaps hit it from behind) -> Veiled Strike (which stuns them if executed from stealth) -> hard hit (hold your left mouse button to charge your attack) to knock them down -> slice with weapons and Assassin's Blade when they are low health.
Next I take Strife in Siphoning tree to help with healing and to get to Agony. Agony is great if you are facing two or more mobs. You can stun one of the mobs from afar and when the other mob gets close go invisible and execute your rotation. You can then proceed with killing the stunned enemy. Strife is also great as a DOT once it gets to level 4 or is morphed.
Since I played Breton I went for Light Armor +magicka buff since all these skills use magicka.
You can also mix in Teleport Strike from Assassination tree to quickly jump to the mob , go invisible, stun, hard hit, Assassin's blade them to death. Depends of what you find sexier :)