Quinn is a champion solidly meant for roam, and Snowball. Her W is an awesome utility for terms of Snowballing. She could catch somebody out and secure a win for the Team really.

Team fighting with Quinn is extremely difficult, Unless you're fully built. You'll be very squishy in team fight's. Her job however, is to snipe out the enemies back line. Quinn's burst capability is INSANE Late game. But the chances of her being bursted are similar.

Quinn is unique because she could turn into a bird (Valor), Valor gains her Movement, and attack speed. Perfect for backdooring. Quinn could make an enemy rage quit with enough harrass.

Farming with Quinn is incredibly simple, Her passive makes it this way. Every couple of seconds Quinn has a Target Mark on a Minion,Champion,or Jungle Monster. It's whoever she is focusing or closest too. It makes her Auto attack damage for the next auto attack do alot of Attack damage, very useful in terms of Harrass and lane trade with the enemy.

(Passive)+E+(Passive)+Q = That is Quinn's best combo in Human form. Does the most damage.

Another Quinn combo is fairly unique that most players don't really know about! it's;
(Passive)than, wait till harrier is 1 second away from cooling down+(Passive)+E+(Passive)+Q

That is a great way to get last second harrass as the ADC Quinn, Considering most ADC's would think that your Harrier is on cooldown, but popping the passive last second will refresh instantly!

Valor doesn't really have a combo it's more of an all in type of technique to secure the kills, and killing the backline faster.

But here is valor's Combo

(Valor)+E+R(AT THE SAME TIME)+(PASSIVE)+Q = That should do alot more damage, because Quinn's ulimate AOE.

For that combo I strongly recommend to smartcast your "E", making it a ton more easier to burst with your R+E+R+Q <--- that is the combo.

For ADC quinn I'll strongly recommend 19 armor pen,9 armor,12 magic resist. Considering her Q+R do a ton of burst in the later levels.

But if you want a very powerful early game I'd say full Attack Damage, 15 attack damage,9 armor, 12 magic resist.

Pro: Quinn adc is an incredible lane bully against ADC's with horrendous early game's. Such as? Vayne. I can't explain! How many Vayne's I've completely beaten down as Quinn! Your kit is solidly meant to completely destroy her in lane. (I recommend 19 armor pen runes against a Vayne), Another ADC she could beat down "If Played Smart" is Draven. Now you're most definitely wondering. How can she beat down Draven? Draven has more AA damage. Well if she gets a first blood on Draven, she could continously snowball him. Draven's passive is horrendous if he dies especially if he dies Early on in game. Quinn can snowball really hard. Another ADC she can destroy in lane is Sivir, and Kog Maw. Now Kog maw is a very op champ but in terms of late game. Quinn can make Kog's laning Absolutely HELL with her passive combo's. Sivir could be a bully at times and she could block your Q and ult. However, she's really vulnerable level 2. And you could definitely go in for the kill and add up to the snowball potential. When Quinn turns level 6 it's best for her to roam mid and get a couple kills.Remember, with nice team cooperation. You could get to any Elo!

Con's: If Quinn doesn't really get Fed, she can't really provide the team with alot of burst when needed. That is why it's best to play Quinn against someone she counters and not someone that counters her. Here are some people that I consider pretty solid counters for Quinn.
*Graves(1): Do NOT, Play Quinn if you're against this champion. This guy is meant to destroy you.He can just Q+R and you're dead. His Wave clear is alot more stronger. He could outfarm you better. His passive makes you do alot less damage. Only play Quinn if you're positive you could beat him.
*Lucian(2): Lucian is a lane bully, however he has 500 range. Yet his E+Passive is completely broken in terms of harrass. Example, Lucian Q+Passive+W+Passive+E+Passive does as much damage as Quinn's R+E+R+Q combo. Not only that He could dodge your Q combo. and out trade you when you try to (Passive)+E+(Passive)+Q, that combo is as equal to Lucian's Q+Passive+W+Passive. Play Quinn only if you think you could survive in lane with him, or if you believe your support is skilled enough to zone him in lane.
*Caitlyn(3): Boy oh Boy, this champion is annoying. 600+ Range Level 1, where as you have 525, however cait isn't made to fight head on, she isn't a duelist. If you could pull your combo's off on her you could easily win lane, but beware! If she could zone you, your lane could be lost.
*Corki(4): Corki's True damage+Q burst+E armor pen+Consistent Ult's= Dead quinn. Do not pick Quinn against him unless you kill him 5 times before 10 minutes of the game.
*Varus(5): Far more bursty than Quinn, Could ult her and kill her when she tried to R to him.
*Ezreal(6): If played correctly, a good Ezreal could nail a Quinn just by keeping his distance and Q. He could dodge her Q with his E and still provide harrass.