So, you want to learn how to play the best champion in the game? Well, You've come to right place. Oh, you want me to describe Ahri to you? Alright, so Ahri is a really seductive fox who likes to play with her pets until they break. Ahri isn't the best you say? Well if Ahri isn't the best champion League of Legends must of disbanded.
We take MR blues so we can survive against other mages since that is the category all of her problem matchups are. We take scaling hp yellows for the same reason. Magic pen reds are on here because they are more helpful than AP reds. As far as Quints go take two AP quints and 1 movespeed quint to compliment Ahri's utility mage playstyle.
Ahri is a champion who relies on poking a target down and then going in for a kill when they are vulnerable. In other words, she teases them until can't take anymore then dives in for what she wants. Playing Ahri is like a back and forth game on cat and mouse.
Poke with your q until they have about 33% health or 1/3 of the bar, then ult or flash to melee range and perform your combo.
Max Q first because it is your main source of damage and harass.
Max E second because the charm duration is increased by every point and it almost does the same amount of damage as FoxFire
Max W last because it is the hardest ability to land and is not crucial to your combo.
Your combo is R E Q W + ignite if necessary.