Hi guys,
First, i want you to know that my english is f'kin bad.
Second, dont think that this guide will make you GOD,
'kay you will maybe do some kills but belive me, if u don't play smart, YOU WILL FAIL !
And third, HAVE FUN WITH THIS OP CHAR x)

Pros:
-Great farmer with passive and Duskbringer
-Fast and have a shield ( Shroud of Darkness) like Sivir's ( Spell Shield)
-Great harasser in early game, when you will update Duskbringer to level 2 or 3
-Good mid/late game
-Have a FREAKIN OP ULTI *q*

Cons:
-Squishy / If focused, he just die =)
-He is an ulti-dependant char, this doesn't make Nocturne useless if on CD
-No more :D He's just COOL !

Greater Mark Of Desolation : Armor penetration, nothing more.
Greater Seal of Vitality : I take these just because i don't have others :X , The extra HP in mid/late game is worth it IMO
Greater Glyph of Scaling Magic Resist : Same as Seals, i have only these ones , but it's woth it too, it can save your life when you are agaisnt some Nukes
Greater Quintessence of Health : MOAR life early game = Less deaths = Good start :D

A classical 21/0/9 build.

21 in offense because an AD need it
And ...
9 in utility so your buffs can last longer :D

PLEASE FOLLOW THE ITEM SEQUENCE ABOVE !
: More HP, AD, and a bit lifesteal. FOR A OFFENSIVE START
OR
: More HP, Armor and Health Regen. FOR A DEFENSIVE START
: You're a squishy char, YOU NEED THESE Crowd Control REDUCTION AND Magic Resistance so don't be dumb, DO NOT TAKE Berserker's Greaves or Boots of Swiftness
(Upgraded later into ) : More Attack Speed, Critical Chance, and Movement Speed.
(Upgraded later into ) : A great mid game item, it gives you Attack Damage, Critical Chance, Armor Penetration and a great Active.
Emblem of Valour (Upgraded into ) : Because you need Lifesteal if you want stay longer in teamfight (or simply not die), and it gives a Team Aura (look at the description), which will help your AD team mates A LOT !
: More Attack Damage and Lifesteal, nuff' more.
: It will help you with the bonus HP, Mana and Magic Resistance. And the Shield added to your Shroud of Darkness is simply too OP :D

Just follow the Skill Sequence above

Paranoia> Duskbringer> Unspeakable Horror> Shroud of Darkness

Exhaust : Great spell if you chase someone or after Paranoia so he can't escape.It can be used against Hard AD characters like Tryndamere or Xin Zhao.

Flash : It helps alot if you want to escape someone or just catch him for this LAST HIT.

Excuse me if it don't helps you alot, but its my first guide so be indulgent PLEASE.
I will probably update this guide soon, because it's not really finished.
TRY IT BEFORE COMMENT OR VOTE !
Thanks for reading, GOOD LUCK!