If you're new to Ahri

This build isn't the typical Luden's with Electrocute build that will grant you more success. If you're brand new to Ahri I recommend going with a more standard build such as that one. Having prior experience with Ahri makes this build much more fun and applicable.

You're intermediate with Ahri

You have finally grasped the ropes of the slippery fox-girl but you're bored of the same old build? Then you've come to the right place. I would categorise myself within this section of the guide since I don't play Ahri the most.

Start of the game: Well typically you either help with wards but on the off chance you're invading it's best to start with E - your charm. This way you can ensure that you draw in an enemy for your team to kill with ease, the downside to this is that if you miss you're screwed and the invade might have to be called off. It's also quite a mana heavy ability if you need to use it multiple times within the first minute, also until you're level 2 the laning part afterwards will be quite a hassle.
If you're not invading then I recommend going for W, this grants you great movement speed and poke which is especially good if the enemy jungler tries to cheese a level 2 gank.
After your first back you will remain to have little to no kill pressure but the Kindlegem along with your W should ensure that you won't die even to ganks unless under heavy CC.
After purchasing Imperial Mandate any form of CC implemented by you will substantially increase your damage along with any teammates. After this purchase rush towards any teamfight whether it's contesting drake, herald or scuttle, landing a single charm should guarentee a kill if you have a teammate nearby.
Try working for teamfights as your main source of gold but that shouldn't mean that you avoid CSing.
After you have bought the essential items 5v5 ARAM is your best bet for winning the game.

Good luck in your games if you use this guide and most importantly have fun!