This is actually a build/mini guide for my friend. Note that I've only played Ahri once for the sake of this build, but I have played this game for a long time and mages are my specialty next to tanks. So again I'm just a first time Ahri player, and none of this probably matters to anyone xD but I'm trying.

What her skills do:

Her passive is every 9 hits of her magic spells (maxing at 3 hits per spell) She then gains a certain amount of spell vamp for her next ability.

Her Q (Orb of deception) Shoots out a big blue ball that pierces enemies and does damage, then returns and deals the same amount of damage, but its true damage this time. It can hit the same target twice so it does some good damage.

Her W (Fox-Fire) Sends out 3 little balls of fire to surround her. After a second they will leave her to attack nearby enemies and i believe prioritizing champions.

Her E (Charm) Blows a kiss in a straight line as a skill shot. If it hits an enemy it does damaga and makes them walk towards her like a stun, but it forces them to walk at her.

Her R (Spirit Rush) She dashes where you are aiming and sends out fox-fires. This can be used 3 times in succession and sends fox-fires for each dash.

I tend to play passive/aggresive, and harrass as well as i can. I realize this may be a little harder with Ahri, but it is possible. I tend to build health/Ability power so I can stay alive longer, and hit at a decent rate. You won't hit hard, but you won't die hard.

I use The Flat Ability power Quints for the raw fire power early game. I use The Ability power per level glyphs for the sheer power. I use Health per level seals for more survivablity considering it gives you about 175 health at level 18. I also use Magic Pen Marks for them tanky people.

I honestly use Teleport and ignite on every champion I play. I use Teleport so I can get around the map as needed for ganks or to save a turret. Ahri I use Teleport and Clarity because early game Ahri tends to be mana deprived in my eyes. You can choose what you wish, but I suggest keeping teleport. I don't suggest flash seeing as how Ahri can just ultimate if push comes to shove. Ignite could work well too, People like warwick, sion, and mundo need to be ignited to be killed in most cases.

Pros:
-She Is really pretty strong
-She has a spell vamp passive
-Her Charm can get someone destroyed
-Her Q does true damage
-Her ult can be used as an escape method

Cons:
-She is mana Deprived
-Charm can affect minions
Honestly thats all I can think of.

Most important thing you can do for your teammates is land that Charm. Its not very hard considering how fast the missle speed is, but it can be a hassle to get around minions. Try, try, try your hardest though,for it can turn the tide of battle in a positive way. I suggest while in lane trying to use it, move around minions a little. It will most likely scare champions unless you pose little threat to them.

There is nothing unique about my build/strategy compared to others. I just build healthy for survivability. If you are good at keeping up your farm and getting kills and assists then it will work perfectly for you.

Get her charm off on an opponent as much as possible to prevent harm to yourself. Spam, spam, spam her skills in a fight. Trigger her passive, and get the health from it and Will of the Ancients. Her Q does true damage so smack away their health all you want, just make sure it hits in the return so it actually can do the true damage.