Take flash so you can easily double hit your Q if your ult is on cooldown. Ghost vs. Cleanse. I prefer Ghost in most cases so you can also easily double hit your Q. It's also a very good spell against CC related champs since you can easily dodge them with Ghost. Take Cleanse however if you're against an Annie. Her stun is pretty hard to dodge and will most probably always have it. Cleanse also removes Ignite. Take note of this. Barrier vs. Exhaust. Barrier is good if you're against a Lux, Akali, etc. You can easily counter their burst damage. Take Exhaust if against assassins that are hard to counter, Zed, Talon, etc. In most cases however, take Flash and Ghost.

Lich Bane's a really good pick on Ahri as you can peel easily and poke during laning phase and late game in teamfights if your ult is on cooldown. Gunblade is also a nice pick. I recommend this instead of protobelt because gunblade amplifies your healing on passive if you're in a tight position. Abyssal Scepter is well for amplifying your damage too. Liandrys is a good pick since you have gunblade which slows the enemy and your charm which is also a disable to double the damage liandry's gives. I prefer CDR boots since you won't have much cdr on your build so take these boots. Rabadon isnt always a good pick. I take it in most cases, Take zhonya's as an alternate if in a hard match up. Take Core #2 If you're not used to Core #1. Core #2 would be an easier choice with easy kiting.

Most Ahri players take this sequence. Max Charm (E) second if your team is low on crowd control.

Thunderlord's Decree is a really good keystone for Ahri since she is a burst mage assassin. I recommend you take Deathfire Touch with Piercing Thoughts if against long range match-ups.

Take these Runes with Cores 2,3 as they will be really good since you have Magic Penetration and your CDR will be full since You have Morello, Abyssal, and Zhonya's. If you're doing Core#1, take 9 Magic Penetration Reds, 9 Health Per Level Browns, and 9 CDR per level Blues, and 3 +5 AP Quints. In Core#1, you won't have any Magic Resist and Armor items, only Health, so might as well go all the way with your Runes.