This is the way I build her, and I know that this is very different to most other guides. The initial potions are to stay in lane, and farm/harass and I will naturally explain the thought process.

Eleisa's Miracle - This item allows you to spam abilities witout having to calculate how much mana is remaining every two seconds. It is very helpful to have and many people overlook it, but it is essential in my opinion to have mana available in critical times.

Sorcerer's Shoes - This gives you a hit of magic penetration, which is always useful. It also increases your speed, which helps in ganks.

Rylai's Crystal Scepter - This item gives you a hit of ability power, which is always handy, and also a big dose of CC. It helps you run away from enemies, chase enemies and even save you to allies who are being chased down.

Rabadon's Deathcap - Now the big time Ability Power is coming into play. This gives you an enormous 140 boost in AP, and also an additional 30% of your Ability power. This item gives you real hurting power, and can make enemies think twice about trying to go 1v1 with you.

Void Staff - This gives you a decent amount of Ability Power, but more importantly you gain a tidy +40% Magic Penetration. This can add some more power against those who have given Magic Resistance a thought.


Zhonya's Hourglass - Another burst of Ability Power, a little bit of armour for survivability and a unique passive which can come in handy in certain situations. Imagine you are in a teamfight and suddenly there is a huge red circle around you. A quick hit of the activating shortkey and you have avoided a nasty ultimate. It can also be used for tanking a turret hit, drawing fire of superminons whilst your towers destroy them or even jumping in the way of someone attacking an ally, and watching them in confusion, unable to land a hit.

Heal: This is a somewhat odd option, as many people choose ignite over heal. The reasoning behind heal is that early game, you want to stay in lane as long as possible. Most other charactersi prefer ignite, but with ahri I think heal is a better option. It also comes in handy when being ganked, as it can give you just enough health to escape the kill.

Teleport: This gives Ahri better laning potential mid. It means if she is losing mid, she can pop back to base, make a quick buy to give a little boost and come straight back to mid in around 15 seconds if you know where what you want to buy is in the menu. This can also be helpful backdooring, as Ahri can uquickly push a lane with her multi-hit abilities. Late game backdooring is especially helpful because at times you can wipe out entire minion waves with just orb of deception and fox fire, relieving pressure if the rest of your team is defending.

Pros
[*] No worries about mana
[*] Spamming potential
[*] Ability to escape ganks

Cons
[*] Lacks ability power early game
[*] If you do not win your lane early game, you will not likely recover.
[*] Loses survivability if ultimate is down

Early game, Ahri is a very good harass with Orb of Deception, letting you also last hit minions whilst chipping away at your opponents health. At level 2 you gain your CC, which you will hit at every clean opportunity, and follow with every other spell you have. Your potions and heal will help you stay in lane until you earn enough to buy giants belt. When you have enough, quickly recall and Teleport straight back, leaving no farm behind and avoiding getting zoned yourself. Eleisa's Miracle now takes over the role of your potions, as you can comfortably now spam abilities without having to worry about mana. Next, and very late come Sorcerer's Shoes, and then you finish the build for Rylai's Crystal Scepter. This gives you immense roaming power, as you can freely run aroud, and as soon as a gank occurs hit fox fire, slowing enemies chasing you and repeat until you are safely behind a turret.

As mentioned in the early game section, you have very good roaming power after getting
Rylai's Crystal Scepter, and also have a triple flash ultimate to escape if you get into real trouble. Here is where you start to build serious Ability Power, but even without you do a decent amount of damage with the combination of your 'Q,W and E' hitting a champ all at once. Ahri is a good option for ganking, with her CC Charm as it not only opens up an enemy to your damage, but the onslaught of your allies. She can also effectively turret dive with her Spirit Rush, hitting twice and getting out of range with the third strike. In team fights, try to stay behind a tankier champion, looking for a weakened enemy to pick out. When one appears, hit a Charm and follow with the usual onslaught.

[*] Only hit Charm with a clear shot
[*] Do not be afraid to use your Spirit Rush to escape a gank (it's better than dying)
[*] Orb of destruction goes slightly further than shown on the ghost image, so if an enenmy is just above the ghost image, fire it and it will deal both the outward and inward damage simultaneously.
[*] Run to the side of a minion wave hitting a turret so you can hit them all with orb of destruction in one use.
[*] When being chased, just run away and hit fox fire when an enemy comes close. Rylai's Crystal Scepter will do the rest.
[*] Count your Essence Theft as it gives you sell vamp every 9 stacks. It is a useful tool, don't overlook it