Quints

Flat ability power

• Increases your Q damage by 9.801
• Your W by 11.88
• Your E by 5.1975
• Your R by 15.5925

• Total extra damage: 42.471

• This is not only important for increasing damage dealt to champions, but also helps you one shot caster minions with your Q

Marks

Magic Penetration

• The best mark for increasing your damage
• Gives you a total of 22.80 magic penetration when combined with
• All Champions start with 30 magic resistance and ranged Champions do not gain magic resist per level. 
• Against a ranged middle lane champion who doesn't have magic resist in their rune page you will reduce their magic resistance to 7.20 once you have

Glyphs

Flat Magic Resist

• Only taken if you're against middle laners that do magic damage
• Reduces incoming magic damage allowing you to win trades

Ability Power per Level

• Taken if you're in an extremely easy match up where you don't need the MR
• Also taken against AD mids
  

Seals

Flat Armor

• I go flat armor now as it helps win trades early on since a lot damage comes from auto attacks. Also, in the current meta bruisers/ADs are very strong and it helps you deal with them.
  

Health Per Level

• A viable option against AP mids
• Ahri is a squishy assassin and this helps make up for that

Flat Mana Regen

• I don't like flat mana regen seals anymore because I start flask, which gives you a ton of mana to get through the early game.
  

Skill Order: R - Q - W - E

• Max your ultimate whenever you can for the reduced cooldown and increased damage
• Max Q next for its damage and wave clearing
• Max W next for its damage
• Max E next for the increase in damage and charm duration

Take charm first if you're invading or fighting at level 1. Always make sure to use your first skill point at the last possible second.

•   will increase your single target burst damage more than .

• Since Ahri is an assassin that thrives on single target burst, it works well with her.

• Some people just don't like having to use a DFG. If that is the case, but you still want to go pure damage then simply buy a after your x2.

Rylai's Route

->

• Get this if you need to survive against your opponent's burst (e.g. Annie)
• You will be doing significantly less damage early on since you didn't rush or , but the slow from can help you secure kills and lock people down that would otherwise escape.

Abyssal Route

• Get this when struggling in lane vs an AP mid (e.g. Vladimir)
• You can get an early and then build x2 and then finish the

- The slow is amazing with your W and gives you the utility needed to prevent enemies from escaping. The slow also helps you peel/kite melee champions.

- It's needed later on when enemies start stacking magic resistance. If there's a lack of magic resist on the enemy team then it's better to postpone this item.

- You get this item for the Unique Active. It allows you to go into team fights and assassinate key opponents then pop the active. This will disorientate the enemy team and lower the enemy team's overall damage per second. I've grown to love this item and can not recommend it enough for an assassin champion like Ahri. Opens up a lot more opportunities to outplay the enemy.

- I almost always get this item every game. It's strong late game when death timers are so long one team fights can decide the outcome of the match. You definitely want to postpone this purchase until later on in the game, but it's great as a 5th or 6th item. The passive is amazing and increases your magic and armor resist allowing you to take more damage in team fights.

- I will usually only get this early on when struggling vs an AP mid. Also, if the enemy team has 2 or 3 AP champions then it makes this item an even better choice. 

- A great item to increase your single target burst. I would try experimenting with it and see if you like it.

- A key item for increasing your overall damage. I would get this after my unless you feel you need a more defensive item.

- They really help healing fast, getting to objectives, as well as team fights extremely fast.