I got inspired by Pekin Woof to use spellbook on Ahri. And went support because is the role I perform better.
Keep in mind that the goal of this build is the utility, as doing damage is a bit irrelevant. You can charm, use everfrost, start fights, and have a variety of spells that can really give your team a great advantage.
I must say I've only played this build on normal, but I believe it can be very strong in ranks.
I normally queue against silver-gold players.
Also make sure you check the notes next to items and skills.

You start Q and try to poke, be careful when you use your Q through minions as you can ruin the wave and even steal farm. Don't forget that gold is super important for you and your Adc. Next get E (charm) and that's where you start to engage and be aggressive.
Normally is around level 3 and 4 that kills. I normally burn ignite first, so i get it back faster. If for any reason I use my flash I like to swap it first for exhaust so I can have it combine with ignite. Ignite comes back up faster so this two spell combo normally give a free kill.

As I mentioned before you should try to swap flash to exhaust, so you can have ignite and exhaust together. Then when it goes back to your normal spells (flash and ignite) try to grab teleport.
Don't forget that you swap spells depending on the situation you're facing, so if you think getting Tp is not a good idea, choose something else.
Example: Drake is up, and you have a chance to steal it, or your jgl doesn't have smite, grab it yourself and secure that drake.