Hi everyone and welcome to my build for Akali!
It is my first guide so I will be happy if you forgive all my language mistakes, because I' m not English...

Twin Disciplines (passive)
Mark of the assassin
Twilight Shround
Crescent Slash
Shadow Dance

If you want see what do each skill take your cursor on image of skill.

Combo:
> Hit > > > Hit > > Hit >

or

> > Hit > > Hit > > Hit >

Balanced Build -- The best build in the world...

Sword of the Occult
Mejai's Soulstealer
Ninja Tabi
Rylai's Crystal Scepter
Hextech Gunblade
Void Staff

Antitank Build -- When you think that is impossible to kill mundo...

Sword of the Occult
Mejai's Soulstealer
Ninja Tabi
Madred's Bloodrazor
Void Staff
The Black Cleaver

AP Build -- When you need a mage or you like Ability Power :)

Sorcerer's Shoes
Mejai's Soulstealer
Rod of Ages
Rylai's Crystal Scepter
Lich Bane
Rabadon's Deathcap

Pick up Long Sword and Health Potion and go with your friend into a bushes as fast as it is possible. Then wait for opponet and kill him! It's very easy with Akali and ignite. If you are lucky you score first blood and gain free gold. You must remember to use your skills on minions and last hits them... it's very easy with Akali too. If you have money for Sword of the Occult and Menjai's Soulstealer go back to base and buy it. Now you can gank with your team in the middle or another side of map... When you earn money for Ninja Tabi buy it immadietly, because it is very important.

In late game you must buy Rylai's Crystal Scepter , Hextech Gunblade and Void Staff. Try to "catch" one enemy, but don't run with him to his friends! Remember! You aren't a tank or God! If you have 20 stacks on two of your stacking weapons... you are God! Now you can (with some luck) kill all their team :) But be careful: 5 champions and turret can be very strong and dangerous and rather don't try it ;/

Don't forget to heal you with your spell vamp.
Remember to use Mark of the Assassin quite often.
In teamwork use Twilight Shround under the enemies. It slows enemies and makes you invisible.
Use Crescent Slash to kill minions and gain money from them.
With Shadow Dance you can kill everything and everyone. Use it on enemies who run away.

Thanks for reading! Plz comment and vote and tell me where I made mistakes.

Good Luck !