Hello Summoners, this is my first full guide. I recommend playing Quinn agressivly, but you'll have to use the E autoattack Q combo to harass the enemy ADC hard.
Use AD or Armor Penetration on Marks. Then swap AD Quints to Armor Penetration if you use AD Marks.
The Mastries are really classic 21/9/0. Skill the Offense tier to AD and the Defense tier to the often used ADC skills.
Quinn is a very squishy strong ADC, her late game is really good when she has got a defensive item so she can get some damage and deal much Damage. My Recommendation is to build from Mid to Late Game a defensive item like Frozen Mallet, Maw of Malmotious or other defensive items.
The agressive items should be attack speed, Crit Chance and Damage. Life Steal is helpful to stay longer alive or to stay longer on a lane
Oh the skill sequence, there I canot say whats BEST at the moment. For a hard harass you should skill his E first. If you want more Damage you should skill her Q. So i'm quite not sure about it but the E seems to be a better choice.
Pros / Cons
The pros are: Easy to learn, high damage output some call her OP, two escape abilities.
Some Cons are: Squishy, You have to land your combo, skillshots.
My Summary for her is a nice champion, a bit squishy, I can farm with her easyly. All in all when you know how to lane and to fight with her. You can get really OP and overpowerd.