This is a guide to tell players how to jungle with Nocturne. Nocturne is meant to be played only as jungler in my opinion. When played correctly and smartly he is unstoppable except by a few things. This guide is here to elaborate on how to do so. I will be working on updating this guide over the next couple of days.
To reinforce just how good this guide is here are pictures:

Pros/Cons

Excellent jungler/Is focused on
Great chaser/Is often played the wrong way
Ult confuses opponents and can be used to get that last hit in/Can be bursted down
Levels quickly/Ult has short range at earlier leavels
Large amount of damage
Ability shield

Even though you can get very fed with Nocturne he can be taken down if he is swarmed or if he is hit by enough cc, since he can block a single ability with his W, Shroud of Darkness. Bad champions to go up against would be Warwick. He can be taken on early game but once he reaches level 6 it becomes harder. If you time your Shroud of Darkness perfectly you can counter his ult, which can bring you down to dangerous levels. His passive gives him health every time he attacks and he can dish out a high amount of damage. Be careful of going up against enemy champions with cc. They can be dangerous since they can stop you from attacking them.

Since you will be jungling take Smite as it is a must have for junglers. It is also helpful, if you are more mischievous, to steal the enemy teams monsters.

Take Flash as well. It is useful for escapes if your abilities are on cooldown.

Substitues:
Switch Flash out with Exhaust so that way it is easier to catch that enemy that is escaping.

First marks:
The flat attack speed from the Greater Mark of Attack Speed helps by reducing the time needed to recharge his passive and is great for making sure that the enemy doesn't have a chance at getting away.
Seals:
The flat armor from the Greater Seal of Armor helps with early game jungling. By giving yourself that little edge it increases the amount of pots used and how many times you need to return to base.
Glyphs:
The increase in critical strike chance from Greater Glyph of Critical Chance is good for chasing and for the lifesteal from your passive.
Quintessence:
Flat attack damage again as an advantage early game. The Greater Quintessence of Attack Damage good for later in game because it adds to the lifesteal from normal attacks and your passive.

Get Hunter's Machete and 5 Health Potions as soon as you start.
Once you return from jungling for a while you should have enough money to buy Berserker's Greaves and a Vampiric Scepter or Madred's Razors, possibly even some wards so the support doesn't have to do everything.
Focus on building Bloodthirster first because of the lifesteal and damage it gives you. Bloodthirster is a snowball item and it snowballs off of minion, monster, and champion kills.
As soon as you have your Bloodthirster, build a Frozen Mallet. This helps for chasing down an enemy and in team fights, as well as providing some well needed tankiness.
I advise getting Enchantment: Alacrity on boots. This gives more movement speed than any of the other enchants and you don't have to stop and hit something to gain a short boost of speed that dies off quickly, probably leaving you the same distance as you originally were from the enemy.
Guardian Angel for trolling the enemy team and staying alive.
Ravenous Hydra for easier monster clearing and minion wave clearing. The AoE also procs life steal so this is a very powerful and good item to have for Nocturne.
Infinity Edge to finish off with because of the large crit chance and the bonus damage on a crit.
Substitutes: Switch out Infinity Edge with Maw of Malmortius. This gives you bonus attack damage along with some magic resist and a shield for when you get low on health, it also causes Nocturne to become more powerful the lower his health is because he gains more AD.
Or Blade of the Ruined King since this gives bonus AD, lifesteal, AS, and a tank shredding passive. The active can be used if you get into a tight spot. The active will heal you for a a percent of the target's max health and steals some of their MS, allowing you to make your get away.

Passive:
Nocturne's passive Umbra Blades grants him an aoe attack for 120% of his current AD and heals him for 10/18/26 health per enemy hit. This has a ten second cooldown and the cooldown time is reduced by 1 sec every time he auto-attacks.
Use this ability when you are in a large crowd of minions. You regain health from every opponent you hit. The more minions hit the more health you get back.

Q:
Duskbringer is a skill shot. When used it creates a line of black smoke. When it hits an enemy champion they leave behind a trail and if Nocturne is in the smoke he gains bonus movement speed and attack damage. He also ignores unit collision if he is in the smoke. This is great for hitting an enemy who is out of Flash distance. Duskbringer can also be used to escape through a line of your minions since you ignore unit collision.

W:
Shroud of Darkness passively grants Nocturne bonus attack speed. When activated he gains a shield that lasts for only a couple of seconds. This shield blocks a single enemy ability. When it does Nocturne gains double the attack speed bonus for several seconds afterward. This is meant to be used defensively. An example would if Caitlyn were readying her ult, if you activate your W and move in between her and her target they don't take any damage and neither do you.

E:
Unspeakable Horror deals magic damage over 2 seconds and if he stays close to the enemy afflicted they will be feared. This can be used to get an enemy away from a safe area such as a tower. Be warned that this could also make them walk towards where they were headed. This ability gains bonus damage from AP. This build doesn't grant any AP unfortunately.

R:
Paranoia is Nocturne's ultimate. When activated everyone hears the word "Darkness" and causes all enemy champions to not be able to see any allies, minions, or wards for a couple of seconds. If activated again Nocturne can rush to an enemy that is in range, dealing damage to them as well. This is a great ability if you have wards set up to see where the enemy champions are. I advise having another character in game that can reveal characters on the map such as Twisted Fate, Kog'Maw, or anyone with Clairvoyance. Be warned that ulting into a team fight could cost you. Where this is great for ganking in can be turned against you if the enemy is anticipating you.

For Nocturne focus on leveling up his Q first because of the boost you get while in the trail it leaves. Second get his E maxed out because of the fear it causes. Then max your R and W. I max out his W last because it gives you the shield at whatever level you are the only thing that gets better is the attack speed boost and cooldown.

The cirlces represent places to ward. Make sure that the wards are placed in bushes so that you can still see the enemy. If the enemy team has a champion that uses stealth (i.e. Evelynn use Vision Wards instead.

Since you will be jungling it will be advisable to get a leash but it is possible to take blue buff, which is where you should start, without one. Continue on to the wolves, wraiths, and golems, in that order. Continue going back and forth until you are confident you can take red buff. Take red buff and feel free to gank whenever. You can do so earlier but red buff is just to help ensure getting a kill. Make sure to go after dragon for the gold. If the enemy team doesn't have a jungler, in which case you will need to help which ever lane is 2v1, feel free to take the monsters from the enemy team's jungle. Beware of enemies passing through to get to a different lane or if they are going for a buff themselves.

Hopefully with this guide you will do amazing and I hope that you all find it helpful. Nocturne is a great character to play as and can become the AD carry of your team if you play smart. If you do so then you shouldn't have any trouble with slaying anyone. Have fun and make sure to leave comments on what can be improved on and what needs to be added.