So you wanna play Nocturne, but you're lost on how to start? Well let me help you. Nocturne's a fine AD champ, and here's your road to victory. I'll let you know some tips and tricks, and lead you on a nice road to victory.

Pros:
-Unstoppable if fed
-Passive gives a natural heal that can keep you in lane long
-Strong chaser
-Has a spell shield to block Karthus ults or other high-damage abilities
-Amazing ganker - ult and fear are deadly in work together.
-Very good for getting or assisting in first blood
-Ult can be used in variety
Cons:
-Can be shut down easily early game by a strong harass or zoning
-Being shut down early game means you're not likely to be successful late game
-Early game reliance on passive can be a problem
-Zoning and harassing combined together can prevent a strong laning phase.
-Must be good with your ult or it'll mean you're not likely to help out.
-Must have great timing on your spell shield or it will be too late or too early for it to block the spell.

The key to a very nice early advantage is one thing - RUNES. Now the ruins I use would be more centered on Armor Penetration or Attack Speed. Everything else is not nearly as worth it. Nocturne NEEDS attack speed, and lots of it. It works well with his passive, which can keep him in lane long enough for him to farm, or get fed. However, you might not like my rune options. You could try getting Mana Regen per five seconds as another option. Nocturne tends to have mana problems early game, and these runes will give him the extra mana regen to keep in lane, or harass. I still firmly believe that extra attack speed is the way to go. So, why not get attack speed marks? Because marks are A) the best runes for armor/magic penetration, and getting armor pen marks can easily get you to penetrate most champion's base armor. Armor pen quints help, but if you feel like attack speed glyphs and seals just don't get the job done, then attack speed quints are always a good back up!

For Nocturne, you should always go 21/0/9. He's mainly an offensive champ, and he needs all that he can get. If you run exhaust, be sure to grab the mastery that improves it. Also, be sure to grab the extra attack speed mastery, and the armor penetration mastery. Building all the way up to Havoc and getting that extra 5% to your attack damage can really help out late game. Be sure to grab it. Now, over in the utility section, you should drop three points to reduce time spent dead, and then a point into the improved ghost. Then, grab the exp buff, and I tend to drop a point into greed, but if you decided that you prefer that you would like extended neutral buffs, or more mana regen, you can drop a point there too.

I typically start out by grabbing a Doran's Shield, though I won't be surprised if you start out with a Doran's Blade. I've also seen people start out with a long sword, though typically they go for more armor penetration than life steal, which I find more helpful. Typically, I get Berserker's Greaves for boots, however Merc Treads or Boots of Swiftness are good ideas too. After that, I go for an Emblem of Valor, for that precious life steal. However, if you're fed, and you can buy a B.F. Sword, DO SO! The B.F. Sword builds into a Bloodthirster or a Black Cleaver, and the B.F. Sword takes up most of the cost. I recommend getting a Bloodthirster before a Black Cleaver, though, because it provides life steal and lots of damage. Either way, if you're not fed, proceed to a Stark's Fervor, if you ARE fed, build into a Bloodthirster. At this point, your items will be Doran's Shield, boots, a Bloodthirster, and a Stark's. After this, take a look at their team. Is there a tank that's doing well and has a lot of health? If so, go straight for a Madred's Bloodrazor. If there isn't do they have a tank that has a lot of armor? If so, get a Black Cleaver. Be sure to sell Doran's shield if you need money for either of those items, or just need to free up a space for a better item, like a Recurve bow, or a B.F. Sword.
Optional Items:
Frozen Mallet- If you feel you're not chasing well enough, or you're being focused down too easily, this is a good item to grab. It gives a very nice health boost, some extra damage, and also slows them with your basic attack. This is really nice for chasing, or just to get that little boost of health you need for survivability.
Infinity Edge - I Don't usually grab this, but if you think you need that extra boost to your punch, and you don't need that Stark's, then you should work on an Infinity Edge. It's really nice all around, and an especially good option if you're fed.
Youmuu's Ghostblade - This is pretty nice because of the active it gives. It can help you chase, or deal out a little bit extra damage faster. It also gives armor penetration, which is a must if there is a more armored up tank on their team.
Guardian Angel - This is pretty nice if you think that you're getting hit pretty hard. It'll revive you if you accidentally get greedy and tower dive hard, or you just run into Caitlyn's ult, or maybe Karthus thought he'd say "good morning" with his ult. It also gives some armor and magic resistance if you think you need the survivability. Remember that the cooldown on the revive is very long!
Banshee's Veil - Very nice for survivability, plus it'll absorb one whole spell every so often! If you happen to be taking most of your damage from a particular spell, then going with a Banshee's Veil can really help. It also really helps if you're bad with your spell shield, however if you're good with your spell shield, this can be pretty useless.

PASSIVE - Umbra Blades - Deals 120% damage to units around you, and heals you based off hom many of them you hit. Very good for laning, and also helps out the life steal.

'Q' Assigned ability - Duskbringer - A skill shot nuke. Goes through minions and walls, and initially does damage. It leads a dusk trail behind. If a champion gets hit by the initial nuke, then they leave a dusk trail behind for some time. While on the dusk trail, Nocturne gets bonus Attack Damage and bonus Move speed.
'W' Assigned Ability - Shroud of Darkness - Nocturne's Spell shield. It does two things. 1) Passively gives bonus attack speed and 2) When activated, if it blocks a spell, it doubles the passive bonus for a short time. The passive attack speed bonus starts at 20%, then goes up by 5% per level.
'E' Assigned ability - Unspeakable Horror - Target takes DoT for a short time, and if Nocturne stays close to them for the entire duration, they become feared for a short time. This can easily help get first blood, or guarantee a kill.
'R' Ultimate Ability ~ Paranoia ~ Nocturne activates his ability to do two things. 1) Cut off all friendly vision from the enemy team. After he does this, he can 2) select a target enemy champion and fly to them, damaging them when he arrives. Note that the cutting off of friendly vision from the enemy team is good for ganking and Nocturne's ult can be used for many things. It can also be used to kill, depending on how much damage you do. Also, be aware that it does NOT have infinite range! You have to be somewhat close to fly to enemy champions.

It's a good idea to start of with Unspeakable Horror first. The fear from it, plus the fact that most champs can't get out of it fast enough, pretty much almost guarantees a first blood! After that, I grab Duskbringer, for its harass, and then the spell shield, for the passive attack speed. I then grab Unspeakable Horror again, and then drop a point into Duskbringer. Since I'm level six, I'll grab my ult, and then from there max Unspeakable Horror and Duskbringer, taking points in your ult whenever you can, and then dropping off points into your spell shield when you're done maxing. Another good idea is grabbing Duskbringer first, and then Unspeakable Horror, then continuing as mentioned before. I don't recommend grabbing your spell shield first, because it doesn't do very much for you. You might also want to take your first point in spell shield at level Seven, choosing to put three points into Unspeakable Horror, or Duskbringer.

What I use:
Exhaust - Good for chasing, or ensuring a kill. Improved Exhaust makes crunchier targets more squishy and easier to kill.
Ghost - Great for chasing, getting back to lane, running, or just getting around quickly.
Ignite - Good for getting a kill that you're not sure you'll get, or just making a target squishy.
Flash - Pretty nice for chasing, or just making a quick getaway. Doesn't have nearly as many uses as Ghost, but it's still handy.

Not recommended:
Teleport - I don't recommend using teleport, but it can still be useful in some cases.
Clairvoyance - No. Just.... No. Leave it for the support champs.
Heal - I don't recommend it. Not as helpful as ignite, exhaust, ghost, or flash.
Clarity - Helpful early game, but otherwise it just takes up a slot for Exhaust or ignite.
Rally - Honestly, no one uses this. I can see you using this, but it's definitely not nearly as helpful as ignite or exhaust.
Cleanse - You've got a spell shield to block Crowd Control. If you're that bad with it that you have to use this, I suggest that you practice some more.
Fortify - You're taking turrets down, not trying to keep them up. Leave it to the tanks.
Revive - I don't like this. If you die often enough to use this, you need to get better.

Be sure to work with your team!! Nocturne is a great ganker, and his ult can be used to guarantee a gank somewhere else. Try to stay aware of what's going on, and where it's happening!

This guide should help you get on your way to a better day with Nocturne! It might help you see what you like on him, or what you don't, and might lead you to make your own builds!

P.S.~ This is only my first build! If you have some tips for me, or just some feedback, leave a comment!