This is my Ahri build! I hope u enjoy it.

Farming 1-10

At lvl 1 just try to hit the whole minion wave and maybe the enemy to get stacks on your passive, auto atack only to last hit the minions.When you get lvl 3 dont try to use your full combo because u will run out of mana really quick, just keep using orb to harrass and auto atack to last hit if you use the orb correctly u will start hurting him and you are not going to lose a lot of mana. If he is beside the minion wave you can use taunt and then orb to do more damage, if he is behind just use orb.Lvl6 this is the moment when you can be more agressive, keep harrasing with orb, and if he is half hp you can use your taunt then orb and use ult then get closer and activate fox fire and Ignite and dash 2 more times.
If you see that your team needs help in a lane you should go and help them to push their lanes faster

For Runes i use:
Greater Mark of Magic Penetration x9: Magic penetration marks are always importan in AP champions, because there are a lot of armor penetration items but there are not enough magic penetration ones, magic pen runes make you hit harder with your spells.
Greater Seal of Armor x9: all the casters have problems with heavy dps with gap closers this runes will make you survive more to their ganks if your ultimate is on CD and someone caught you.
Greater Glyph of Scaling Ability Power x9 : Ap per level glyphs, these gives a nice amount of AP , in early game flat ap glyphs are better but ap per level gives much more ap in mid and late game.
Greater Quintessence of Scaling Ability Power x3 : More AP per level runes, like the glyphs per lvl these gives you large amount of AP in mid and late game.

Abillities

Essence Theft
Passive
Ahri gains a charge of Soul Eater whenever one of her spells hits an enemy (max: 3 chargers per spell). Upon reaching 9 charges, Ahri's next spell has a 35% Spell Vamp.

This is a really useful passive and will make you stay in lane longer.
Use Orb of Deception to stack it and to use it.


Orb of Deception
Ahri sends out her orb, dealing (40/65/90/115/140) (+(0.33 per ability power point)) magic damage, and pulls it back dealing (40/65/90/115/140) (+(0.33 per ability power point)) True damage.

The main damage you will make is with this ability. Use it to stack your passive and when you reach the 9 stacks use it when the minions are coming so you can hit all of them.


Fox Fire
Ahri releases three fox-fires. After a short delay they lock on to nearby enemies (prioritizes champions), dealing (40/70/100/130/160) (+(0.38 per ability power point)) magic damage. Additional fox-fires that hit the same target deal 50% damage [max damage: (80/100/120/140/160) (+(0.75 per ability power point))].

With this and with Orb of Deception you can reach the 9 stacks in just 3 abilities.
It doesnt do a lot of damage to a single target because in teamfights you dont know where the foxes are going.


Charm
Ahri blows a kiss dealing (60/90/120/150/180) (+(0.35 per ability power point)) magic damage and charming the first enemy it hits, causing them to walk harmlessly towards her for (1/1.25/1.5/1.75/2) second(s).

A good taunt this will be your initiator when you want to kill someone, its a skillshot so you need practice to land it. At lvl 5 the taunt is of 2 seconds that is enough time to release your combo.


Spirit Rush
Ahri dashes forward and fires essence bolts at 3 nearby enemies (prioritizes champions), dealing (100/140/180) (+(0.3 per ability power point)) magic damage. Spirit Rush can be cast up to three times within 10 seconds before going on cooldown.

Her ultimate, it does a good damage, help you chase your enemies, escape from ganks, and helps you to find a good place to shoot your skillshots while doing damage.

Using your abillities

Soul Eater (passive)

If you learn to use this you will stay in your lane until you want to go back. Using this in a appropiate way you can heal all the damage your opponent is trying to do. You can stack your passive while harrasing and farming. Using Orb of Deception you can get 3 stacks really fast, then use Fox Fire and you will have another 3 stacks, finally use Fox or your orb to reach the 9 stacks.
When you reach 9 wait until a new minion wave comes, when the minion wave is in a straight line coming use your orb to hit all the minions so you can heal you all you can.

Orb of Deception ( Your Q )
This is your main damage ability if you manage to hit 2 times with it. Remember that when the orb returns it makes True Damage :D.You should harras the with this while hitting the creeps to last hit. It has a nice range so you can cast it from behind your caster minions but remember that if you are too far the enemy will have time to avoid it.Use this to heal yourself with your passive.

Fox Fire (Your W)
This spell has good damage and its not a skillshot but you dont know where the foxes are going because they prioritize champions but in a team fight you are not going to be sure if they are hitting the tank or the carry.In lane phase is easier to land it because if you go near your enemy you will hit him with the 3 foxes. (each consecutive fox deal 50% less damage) You can use this to pop an enemy Banshee's Veil

Charm (Your E)
My 2nd favorite skill of Ahri (1st one Spirit Rush ) Its a long skill shot taunt but you will need practice to land it correctly. Its the initiator of your combo so if you want to hit with all your spells you cannot fail this taunt.If you are against a melee (its strange to see a melee in mid but there are games when an auto-atacker is mid) to last hit minions he will need to walk to the front of his minion wave in that moment when he is about to last hit use Charm then use your Orb of Deception with Fox Fire, do this every time he tries to last hit. If you are against a caster use it when they are out of place.

Spirit Rush
3 free flashes and great damage to 3 champions with each dash. With this you can chase someone to taunt him, escape from ganks and to do damage to the enemy team while you focus their squishiest champion with the rest of your combo.It can help you dive turrets easily, just harras with your other spells and when he is low hp you use your combo and dash against him if he runs to his turret dash again to get him as low as you can (or kill him) and use your Ignite to finish him, use the last dash to escape from turret range

At level one i take a point in Ahris Q so i can farm as my guide sais (max this as soon as possible)
At level two i take a point in ahris E to stop the enemies from escaping from fights (Max this second)
At level 5 i take a point in ahris W to farm (Max this last)
At level 6,11,16 I take point in ahri ulti To deal heavy damage