I'll copy paste this from another thread about the same topic.
I actually prefer laning with him and it works out really well. Not the best harass but if even a small opportunity opens to kill someone in a lane, you can bet he can do the job perfectly after level 2 and having Q and E. Max Q then E then W putting points into ult whenever possible ofcourse.
Zerk Boots -> Rush Brutalizer -> Best Friend Sword -> Starks -> Zeal -> Black Cleaver -> Ghostblade -> Phantom Dancer -> Infinity Edge
Starks can later be sold for a Bloodthirster if you're hurting and need some better life steal but not really necessary. Build heavy AS with AD as you can take it. Proc your passive as often as you can not only for the heal but minion clearing. I have only lost 1 game with this build and I played him all day. The 1 game I lost I went 16-7 and no one on my team got more than 2 kills. Even the enemy team said they were only scared of me and wouldn't initiate in a team fight if I was around.
Oh and if anyone hasn't told Shaco yet, tell him to move over. Best gank in the game just got a new name. Nocturne will make your heart skip a beat if you're low health and your screen goes dark.
EDIT: Okay so after a few more days of toying around with him, ive found that my build has changed since I can work better with him. Once ganking and using your Q in conjunction with your passive to wipe out minion waves comes easy to you try this out.
Start with Cloth Armor + Health/Mana Pots(I prefer mana for more harassing since your passive is plenty of heal)
Rush Wriggles -> Zerk Boots -> Infinity Edge -> Zeal -> Black Cleaver -> Frozen Mallet -> Finish Phantom Dancer
The Frozen Mallet can come a little earlier in the build if you are being focused a lot but I recommend going straight for IE and Zeal. Know when to get into fights, use your spell shield wisely! I cant stress how important that spell shield can be. Do NOT ult onto a gank unless the entire team is accounted for and you know for a fact you can shut them down. A lot of Nocturnes im seeing are ulting onto random people then crying that their team didn't follow them after they got counter ganked. Dont be afraid of a tank unless its late game with full builds, you can still chew through them pretty easily unless they have a decked build.
Cheers all! Hope this helps for what is slowly becoming my new favorite champion. Cant get enough of the playstyle. Also dont let anyone tell you hes a bad farmer. His farming ability is insane when you can line up a Q and hit the right minion to proc your passive on the entire batch.