. Anyway, I main Quinn as my main ADC and I used her from Bronze 4 to Gold 3 in pretty much about 2-3 months. I bought her once she came out and thought she was op, which made me even happier when she got a buff right after. I believe Quinn focuses on assassinations and burst, even for an ADC. This is also my first guide so bare with me.

movement speed steroids. She has a good disengage and can win trades with her Blinding Assault. She also has her Heightened Senses which can prevent ganks with its vision. Her tag team+ Vault is also an extremely great gap closer.
making her Quinn's direct counter. Her tag team makes her melee so it can make it extremely hard to position yourself correctly. This also makes her turn into a front line. She can be extremely hard to play. Sometimes, when Valor is marking an enemy while you use your Vault, your Harrier doesn't apply to the person your Vaulted on.

could also alternate your Greater Seal of Health seals for Seal of Armor instead. The Quints of Life Steal will be EXTREMELY useful for high sustain in lane after grabbing a Vampiric Scepter. I also have a crit mark just to test my luck for good last hit/trades. The rest is standard runes.

The defense masteries will also help you sustain through lane. It is mostly standard masteries you would usually get.

a lot of early damage that follow up to late game. It can also crit with your passive practically deleting them. Infinity Edge is my first item because it gives you really high burst with your passive. After that, I would get Statikk Shiv. This will help you get off the crits you need for Infinity Edge. If their team is building a lot of armor you should go for Last Whisper. If they are building a lot of health, go for Blade of the Ruined King. If they are all damage and mostly squishy, it would be better to get Bloodthirster. These three items can vary in which order you want to purchase them. You should keep a Last Whisper in your build every game unless they absolutely aren't building any armor, in which case you can just grab the other two. Lastly, you should get a Phantom Dancer because it will help you to keep damage on the enemy in fights. It's ghost ability also helps you catch up to enemies that you want to clean up with your ulti. This is what a perfect and easy build would look like. However, obstacles do come around and you should check the situational items listed above.

because with really high level play, you should be able to pull a Harrier+basic + Vault + Harrier+basic. This maximizes your trade potential and cool downs so you can continually do this. Although you should max Blinding Assault because it will help harass more and do more damage. Your Heightened Senses has a great passive giving you a good attack speed and movement speed steroid, so max that second.

Harrier is Quinn's passive in which Valor marks an enemy. If you attack the marked enemy, it will deal bonus damage. This can be used effectively with your Vault to do a huge combo. It also gives you attack speed after you attack if you have at least one point in your Heightened Senses
Blinding Assault is a skill in which sends out a blinding nuke. It is a very solid source of harass and the blind is very useful in trades or to stop the enemy from farming. This will save you countless times.
Heightened Senses is a skill in which gives vision in a radius. Its passive gives you attack speed and movement speed after you land any successful passive with increases per skill-point.
Vault is a skill in which Quinn jumps onto an enemy and leaps off of it, interrupts enemies, and stopping at her max basic attack range. This can be used effectively by jumping off an enemy while standing next to it to disengage and/or kite. After you jump off, they will be marked with Harrier. This will save you a lot more times than anything else. You can use it in response to any pulls or ganks. This can also interrupt Miss Fortune's and Katarina's ultimates.
Tag Team is a skill in which Quinn switches out to Valor. While Valor, you have increases movement speed and attack speed creating a large steroid while chasing or running away. However, while in Valor, she does not have Harrier coming because you ARE Valor and when you use Vault, she does not jump off the enemy. This means you can use it to close gaps.

Ignite + Flash if you're feeling dangerous.

all I have to say other than do what you regularly do when last hitting as any other ADC.

enemy ADC and/or support. You should approach this by first seeing who their support is. If it's an offensive support Leona, just simply basic attack whoever is marked. Nothing special after that. However, if it's a Sona or any passive supports, you should approach this by throwing your q at the target. This will reduce their damage for their trade (or completely nullifying it). Right after you shoot your Blinding Assault, land a basic attack to proc your Harrier, then go straight for your Vault. After you bounce off, your Harrier should come back to the target, so you attack them again. This will deal a whole lot of damage.
If their lone ADC is farming bot with no one around, use your ult to dash up to them. Use your Vault to close the gap and go for the Blinding Assault to stop them from dealing damage. You should be continually basic attacking because you have a huge steroid and take advantage of that. Your tag team is based on missing health so you don't want to use it too early. If they try to run, your MAXED Vault should be up real soon so you can close the gaps again.
high burst. I find Quinn as a more up-front champion because your tag team makes you melee and your dash brings you forward. So you should try to blind as many people as you can. Try to focus the squishies, but attack anyone that your passive touches. This allows you to get an attack speed + movement speed steroid from your Heightened Senses passive. If some people try to focus you, just use your Vault to disengage.