Ahri is a high-burst-mage with a lot of movespeed so u should be always aware of ure capabilties.
In the early game: your top priorty is 2 push and keep ure lane warded her Q is lvl 1 pretty strong with tlords combined and make her a cheesy trader with alot dmg early on. So try keep that in mind and focus all on that.
Nr1 Q the wave at opprtunites where u can hit an enemy
Nr2 Never use ure w too farm, only under tower because of the mana cost
Nr3 Dont miss ure charm or use it carlessly, beacause it decides on u winning a trade or not
Nr4 Keep it calm! U have time on ure R, so Dont spam it! The first dash is too go in, the second is to get a little distance/doge burst and the third is too rengage with ure spell rotation up again too finish the deal
Nr5 Dont loose ure **** when u get ganked most of the time u have your ult up and maybe flash so use those, maybe u can even kill someone, when someone is low (who awaits a person to make a reengage when there are 2 ppl there ^^
Nr6 When u run, always Q behind u because as long as ure Q travels u have increased movementspeed and when u Q behind it logically has a longer travel time.