I'm posting this because I haven't had much success with the other Dominion Ahri builds so far, and this one has worked out well for me. As with any build, take it with a grain of salt. I'm no pro. This isn't supposed to be a bible, but more of food for thought.

Ahri is squishy as all hell, so this build aims to make her a bit tougher. Mostly I've been using this while fighting top, but I've had success with it laning bot as well.

Comments, suggestions, and otherwise helpful criticisms are appreciated. I'd rather hear why you think something sucks than just hearing that it sucks!

Runes: CDR, MP, move speed, and HP.
Masteries: Standard 9/21/0, obviously going the spell side of Offense.

Ahri needs low cooldowns to keep her alive (Spirit Rush and Charm) and to do damage (Orb of Deception is nuts). With the 9/21/0 masteries and celerity runes, you get over 20% CDR at 18 not even counting items. The bottom of Defense helps keep you slippery, with extra run speed and disable resistance.

Otherwise, since she is so squishy, we want to make sure to stay quick and nimble and give ourselves a bit more time to escape if attacked.

In summary: QWE at the start, then Q -> W -> E.

1. Orb of Deception (OoD) does true damage, so we max it first.
2. Fox-fire is good for kiting, bursting, and you don't have to aim it. Hooray! Get this second.
3. Charm is deadly, but one point does most of the work. Charm interrupts channeling, pulls enemies helplessly into towers for 1-2 hits, and otherwise screws with people from quite a distance (if you have LoS). But it does all of that at rank 1, and higher ranks don't lower the cooldown, and whereas a 2s charm is much better than a 1s charm, it's not better fast enough to warrant giving up Fox-fire.

Orb of Deception is ridiculous. Mid-late game, it will 1shot caster minions so you can clear waves in seconds and get rich from last hits. It'll tear chunks out of enemy champs, while you hide behind friendly minions. And it's super cheap to cast! If you have a clear LoS to use Charm, do that first, then OoD while they slowly walk toward you.

Fox-fire is similarly cheap and is good for building up your passive. It doesn't stop you running so... use it while kiting.

Charm requires a bit more aiming, since it hits the first thing it touches. If you're fleeing, it should be an easy shot. Take it and keep running. If you manage to catch an enemy champ with it in a fight, don't waste it! When they're running straight at you and can't dodge, throw an OoD.

Ahri, true to those fox-legends, is a kiter. If she gets into a close-range fight, she will die, pretty much guaranteed. She is also awesome at clearing huge waves of minions.

Push whenever it's convenient. Go around the rim of the Dominion wheel instead of through the speed buff, just so you can throw an OoD at the enemy minions in the lane. It'll get you cash, yes, but also anyone who refuses to acknowledge that minion control is essential in Dominion still hasn't played it enough. Trust me, you'll want those minions around to be your meat shields.

To stay alive in fights, hide behind said minions and friendly champs. Dart in with a charm and OoD and then get out. Ahri cleans up vs melee champs, since she can Charm and OoD from a distance and cast Fox-fire while kiting. Anyone chasing after you in a straight line is just asking for an easy skillshot.

Don't waste your ult. Each of its 3 casts throws 3 spirit bolts (sort of like Fox-fire, but one per target), but don't get overzealous; if you dart into a fight to land all the bolts, always (always!) save the 3rd for darting back out. You never want to stay in melee range pretty much ever! Don't forget that you can use your other abilities between darts, so you can make Charm more likely to land while closer, then dart away before the OoD.

If you're low on health, make sure to take advantage of your passive spell vamp on nearby minions. Minions will start dying in one hit to your OoD's true damage, so you can rake in the cash. You get 3 out of 9 charges toward your passive with each cast of OoD and Fox-fire.

Watch your *** and be wary of pincers. Don't go traipsing through the middle unless you have your ult up, or are otherwise sure that the enemy team is all accounted for. Ahri needs room to run or she'll get crushed. So give her room to run; watch the jungle, stay away from fog of war, check bushes with Charm, etc. Seriously, don't facecheck the bushes. Use Charm. If you do get cornered, I hope you have your ult up so you can dart through walls and into the jungle, then throw Charms behind you to slow them. If you have Rylai's, Fox-fire can slow up to 3 pursuers for the full amount (see below).

Other builds seem to frontload the spellvamp, but this hasn't worked out well for me. Instead, I get boots and Prospector's Ring out of the gate. I used to take Tear of the Goddess but found that my spells just weren't cutting deep enough early on.

Depending on who you're up against, take Sorceror's Shoes or Mobility. I still think Dom is all about speed, so I usually can't resist the Boots of Mobility. Since she's such a great kiter, you can dance circles around melee champs, and of course it gets you back in the action faster when you B or die. The loss of MP from Boots of Sorcery sucks, but OoD is mostly true damage anyway, so it sucks a little less. Abyssal Scepter plus runes will usually be all the MP you need.

CDR is important because Ahri will die without her E and R. E lets you escape most 1v1 fights, and R will dash through walls and away from towers to safety. Naturally you want these up as much as possible. If you aren't going up against AD champs, consider Morello's Evil Tome for the CDR and AP. If you are, Glacial is a good bet.

Get AP to bring up your damage so the spell-flinging actually does something. Then tailor your items according to the enemy team makeup. Remember that each Fox-fire counts as a single spell for on-cast items like Rylai's, so get that earlier if you find you're missing a lot of skillshots or can't stay out of reach of enemies.

I think these are really up to the player and their preferred style, but I always take Ghost for Dominion, and recently Ignite for finishing people off.

Again, I think this is more about the player. If you have trouble laning bot, try Promote. If you get cornered more often than you can handle, get Flash.

With her two skillshots and ultra-squishiness, Ahri's not for everyone, but this build has brought me plenty of joy so far. I hope it helps.