This is my fisrt attempt at a guide, hope you find it useful. Before I get screamed at for being a noob and knowing nought what I speak of I just want to say this is a build that's worked really, really well for me (regularly 20+, 30+ kills a game), I'm sure there are more experienced players who will contest this build but give it a try, see what you think, leave a comment!

So why should you spend your ill-gotten ip on Nocturne, after all 6300ip is a LOT for any champion. Well firstly and most importantly, he's FUN! He's also very well designed, kudos to riot.

Nocturne is a melee DPS character that at first glance is highly specialised at one thing; ganking, but on closer inspection is actually very flexible indeed, he's a champion that can respond usefully to a lot of different tactical situations in the course of a single game.

This is a LANING build, I have tried a jungling and while Nocturne is very good at it, I find that it puts a lot of pressure on the guy who's laning 1v2, sometimes you can even lose the tower pretty early as a result. My advice; keep the jungling for premade games.

PROS:

looks like a badass
sounds like a badass
probably smells like a badass
excels at both jungling and laning
all his powers can be used both offensively and defensively
strong melee dps
almost spammable ranged nuke
2 second fear
skill shot spell shield
all his abilites have secondary effects
passive provides lifesteal and strong farming ability

Paranoia the coolest ultimate ever, turns you into a ganking machine
opponents will flame you for your ultimate (their own fault), and sometimes when you use your ulti for a chase members of your own team will flame you for kill stealing (if they could have caught them, they would have done already, so don't worry).


CONS:

squishy (runes can help a lot here)
can struggle in late game team fights
not great at escaping without ghost or flash
he can sometimes look like a lobster on amphetamines

Greater Mark of Desolation - standard DPS

Greater Seal of Armor - allows me to play very aggressively early game, with Ignite you have an excellent chance of bagging first blood and the gold that goes with it, make sure your laning partner knows what you're upto.

Greater Glyph of Cooldown Reduction - you want to get your ultimate as often as possible, it defines the way you play with nocturne, without it he's just another melee dps.

21/0/9 not a huge lot to say really, I haven't experimented massively with these.

This is where it get's a bit interesting. PLEASE NOTE: As with all champions build to the situation, be flexible, for example I ofetn switch the order of the bruatliser and Sword of the Occult depending on the situation. If you're facing some tanky enemies maybe switch your Bloodthirster for a Black Cleaver, or if you're really pwning and there are some squishy enemies, perhaps go for an Infinity Edge instead, and maybe a Phantom Dancer instead of a Guardian Angel. I can't stress how important being flexible with your build is, games can be won and lost on careful choosing of items.

Remember to use the Youmuu's Ghostblade's active, use the keyboard to trigger it, dont mess around with the mouse it takes too long. Use it just before combat and you wont lose often.

Some people go for shroud of darkness first, I prefer duskbringer, it gives you great early harassing ability and you can nuke both enemies in a 2v2 lane which is great in level 1 fights.

Combos:

Lvl 1: Q - Auto attack - Q - Ignite

Early game: Q - E - Auto attack - Q - Ignite

Lvl 4 onwards: Q - W - E - Auto attack - Q - Ignite

Use your ultimate as a chasing tool and when necessary as an initiation tool (1v1 situations it pretty handy).

Once you get the ghostblade:

Q - W - Ghostblade - E - Auto attack them to shreds - Q - Ignite

Very Early game Nocturne is very powerful, especially with runes, dont be afraid to be aggressive in harassing your opponent, even if you can opnly get someone to go base, that's an advantage as you get a little jump on them in gold an xp. I find it amazing how many people dont take into account ignite in those early fights and stay that little too long in combat, only for you to finish them with Ignite. Though nocturne is an awesome ganker NEVER NEGLECT FARMING! YOU ARE NOT ABOVE IT!

You can be aggressive upto about level 4, then you want to be more cautious as enemy champions will have caught up somewhat.

Many people go base as soon as they hit level 6, but with nocturne you're missing a great opportunity. If an enemy champion (especially a squishy) is on half health or so and doesn't have a Heal, harass him down to low health with Duskbringer. When he retreats behind his tower to go b watch for a bit of separation between him and his partner. Then pop Ghost, Paranoia, launch at him and kill him with Ignite, run away from the tower and round towards the river immediately to get away if you have mana pop Duskbringer to run even faster ( Duskbringer and Ghost are a great combo), DO NOT RUN BACK PAST THE TOWER, YOU WILL DIE. However be careful of enemy CC powers as you probably wont have enough mana to use Shroud of Darkness.

If you're facing tanky enemies, probably best to forget it, go b @ lvl 6 and start looking for ganks!

This is where Nocturne really excels.

After going b you want to rush mercury treads and hopefully you'll have enough gold for a Long Sword. Now look for those ganks. Some people use Paranoia as an initiation tool, avoid this if you can. Only use it if you see a really juicy gank where time is of the essence. It's actually far better to save it and use Paranoia as a chasing tool to finish enemies. Remember it also doesn't do as much damage as you might think so be careful, it's a mobility tool more than a nuke.

In a pinch it can be used as an escape tool too, either by reducing enemy vision so you can juke them (difficult), or by flying to an alternative enemy to escape a gank (also difficult). Your best escape tool is a combining duskbringer and ghost, even with an Exhaust on you Duskbringer should give you the edge in speed to escape.

Now if you're getting kills easily go for Sword of the Occult asap and build those stacks, make it your primary objective, after you get about 8 stacks you'll be fairly dominant in combat. If however things are a bit tougher or the enemmy's playing hard to get go for the brutaliser first.

Remember to get both buffs as often as you can, they make a big difference with nocturne.

When teamfights start to break out, you don't want to initate with Paranoia, it can be tempting, but don't. You'l die and lose those stacks you worked so hard for (very bad). I find it best to observe from the jungle where you can still harass with Duskbringer. Either stay back behind your tank or in the jungle and harass with Duskbringer, when you see an enemy on low health, get ready, if they try to retreat wait till they're just out of range of help and kill them with Paranoia. If an enemy overextends in a team fight use Unspeakable Horror to fear them so you and your team mates can squash them fast, sometimes this is enough to cause the enemy team to retreat, use Paranoia to kill any stragglers. Remember to push those towers throughout the game, towers destroyed makes ganking much easier and is key to winning.

This is where things can get hard, I believe that the longer the game, the worse it is for nocturne, eventually your enemies will catch up and suddenly you might feel a bit squishy, this why I like to take Guardian Angel, it gives you a crazy amount of survivability and with buffs you should be kicking out plenty of damage. The biggest advantage however is when you die and the angel revives you, you dont lose your stacks! With your Bloodthirster (remember to farm like crazy when you first get this) and Sword of the Occult (when you get that 15% speed boost at 20 stacks, you know it was all worth while) the ability to keep stacks is incredible. Remember however that it only works every 5mins so when it's down be cautious.

Essentially late game you want to play Nocturne as more of a carry, with banshees veil and Shroud of Darkness he can absorb 2 cc effects (which is massive) and can turn a team fight.

NOTE: Do not underestimate the usefulness of Shroud of Darkness, ALWAYS be ready to use it, it requires a fast finger but it is capable of blocking almost anything. Be generous with it, intercept ashe's Enchanted Crystal Arrow for example, pop your W and watch it bounce off you harmlessly saving your teammates, caitlyns Ace in the Hole is another great one to block. Your W skill can block their ultimate, and give you a huge attackspeed bonus to boot. It is AWESOME. Practice it, do not neglect it, it is the key to being a top nocturne player.