Pro's
1. Amazing burst damage even early game
2. Very good escape abilities
3. Excellent harass abilities
4. Becomes nearly impossible to escape her after lvl 6
5. Has acknowledged by riot a 'Flippin Ninja" (see her natural buffs while playing her)

Con's
1. Target above most other units
2. Squishy
3. VERY HARD TO MASTER

My name is brahmzy, this is the first guide I have written so do not be to hard on me, now to Akali, I have been playing Akali for about two months now and she is my favourite champions in the entire game this is because she is one of the most op assassins in the game assuming you know how to use her, early game she can only burst down squishy targets but after about lvl 16 she can bring down tanks. that said she herself is SQUISHY so dont think you can engage three people and expect to win, that is unless you are fed =D

The runes have been set up so they activate your passives before you buy a single item, you do not need as many Seals Of Greater Potency, Glyphs Of Potency or Greater Quintessence Of Potency but MAKE SURE THE ABILITY POWER YOU HAVE ADDS UP TO 20 however you should not swap any Greater Marks Of Strength or you will not activate your life steal passive removing ALOT of your early game survivability

The item build that i have should be changed a little bit depending on who you are fighting, for example if you are playing a game and not getting any kills Majai's Soulstealer becomes useless so invest in another ability power based item or if you are fighting against a ranged champion who is doing a lot of damage swap the Majai's Soulstealer for some armour to counter their damage however do no not swap anything but the Majai's Soulstealer unless you really have to as it may severely hinder your damage output late game. another example would be if enemy's are always narrowly escaping you rush the Boots Of Swiftness and so on however when playing against a tanks with no squishy unit to feed off always get an Amplifying so you can get some kills or it will effect your late game performance. Another thing to remember is that people with sometimes buy items that reduce magic damage, if it is just one or two of the champions you are facing you can just ignore it however if any more than that start getting magic resist consider investing in a Haunting Guise, Abisil sceptre or Sorcerer's Shoes.

you should stick to the skill sequence exactly as I have it, the only one thing you should change is very early game and you feel as if you can get a kill instead of getting the Twilight Shroud (your one and only defence mechanism) get your cresent slash first but remeber you will become very vulnerable without your Twilight Shroud.

DO NOT BE AFRAID TO USE YOUR ABILITIES ON MINIONS!
why? because Akali is energy bases and she get 20% heal from spell vamp which requires you to cast spells and since she runs off energy it takes10 seconds to get back to max energy and on top another 10% passives heal from the amount of physical damage you do, so what is bad about using spells on minions? nothing

Your basic skill sequence should be


Mark > Shadow Dance > Twilight Shroud > Crescent Slash > Hit then rinse and repeat
(note that if you have Lich Bane 2 hits occur meaning, 2x your AP.)

Akali is a very squishy champion but she has a HUGE damage burst especially late game, is she is used properly she can easily make win the team fight, however their are certain rules you must follow in a team fight because you must leave as soon as your target is dead.
1.NEVER TARGET TANKS - it doesn't matter what stage of the game it is never target tanks because they don't do nearly as much damage as other characters and they are harder to drop.
2.NEVER INNATE - remember you are squishy so it is suicide to initiate any team fight.
3. Always Target the people with lowest health (excluding the tank)
4.LEAVE AS SOON AS YOU GET YOUR KILL - i know have already said this but it is of the utmost importance because she is targeted because of her high burst damage and will be destroyed if in the middle of the team fight for to long.

In ranked games, you MAY want to build a little tankier, even after the rylais. My first suggestion would be to build up your resistances, because you wont need a crazy amount of health. Your best bet is switching the Mejai's Soulstealer for a late game guardian angel (Magic and Physical Resist), or even for an abyssal scepter (magic resist and magic penatration bonus). Take advantage of that last item and tailor it to the game you are in
In a ranked game, it is likely that you will have a jungler, in which case you should take the solo lane. You are really potent as solo lane, all you really have to do is turtle back until level 6, then take advantage of your cloud to harass them. When the teamfight phase comes around make sure you target the squishy dps heroes or the casters (as they likely will be dealing the most damage and you want them dead A.S.A.P).

Akali is a brilliant champion however she is extremely difficult to master targeted above most other champions however once you master her expect games going positive 10-20 kills and countless assists.