Build on Nocturne with
-Team Fights
-Skill Sequence
-Items
-Masteries
-Spells

This is an important part of the guide, Nocturne is not one to start a team fight. In my opinion, he is awful in team fights. Nocturne can be the finisher of team fights to catch people that run away with a small portion of health left. After the team starts a fight, ult in so they will not draw attention to you and pay attention to their tank while you attack the weak ones.

Nocturne has an important spell for early game, Dusk bringer. Upgrade this spell and it will do plenty of damage against squishy champions for harassment. Upgrade shroud of darkness because you mainly want its attack speed bonus. Its cool down can also be helpful for enemies that will harass with spells. Unspeakable horror does not need to be upgraded because if your attack speed is fast enough, you can attack while he is feared for that short time.

First your probably wondering, "That's stupid why would he get lantern if he isn't jungling?". Wriggles Lantern gives you a small life steal, armor, and minion damage. If your team needs somebody to defend the nexus, nocturne is good for fighting off minions or pushing towers. For early to mid game, you wont have a life steal if you don't buy the lantern, so until you get the bloodthirster, you can take more champions 1v1.
Second is mercury treads, nocturne is a little bit of a chaser, so this is good to have for extra magic resist and CC.
Third is Banshees Veil, this is a great item for teams with magicians. It will help more in the late game while ganking.
Fourth, you need some damage, and the blood thirster is great because Nocturne can farm well and gain the stacks quickly.
If the team is tanky, go black cleaver first, if its more magicians, go ahead with infinity edge. This way you can critical strike them to death, and possibly get phantom dancer after that.
After you build all of this and you still cant win, try switching and selling the lantern for madreds bloodrazors, if the enemy team stacks thorn mails, this can be a good way to fight agaisnt it.

The Masteries I have chosen are all about offense. Nocturne needs to be a quick hit n run champion that can kill the enemy quick as possible. Utility mastery's are useful because Nocturne should farm for quite a long time until he can use his ult and gank.

Ignite is one of my favorite spells to finish off the runners, for nocturne, it is another great DPS on the enemy. I did not choose to jungle because his level and farming can do better in a solo lane. Ghost is used for mainly running. After you use Paranoia on an enemy that is alone, be careful of other champions that could be close by. Ghost out to avoid death.