Hey there,
I´m a Main ADC on EUW and currently between platinum and diamond.
I really love my role as an adc and want people to have the same nice experiences as I´ve got. Due to the major changes to ADC´s and every champion at all with the Runes-Update i want to release this updated Vayne Guide for the patch 7.23 (i´m going to keep it updated if the next patch does any changes to her playstyle/build).
So have fun with my guide and learn what you wanted to know.

Pros

Really strong snowballing
Unbeatable 1v1 potential in lategame
Condemn for CC really useful as ADC
Hard DMG against any kind of opponent (True dmg W+Max HP)
Outscaling nearly all ADC's
Unlimited skill-cap (the better you know her the more you win - every game you will improve)
Playable in every Elo

Cons

Weak early Game
Once behind hard to come back (due she's an All-in champ)
Really squishy before getting BT
Often banned in higher Elo´s

So at first you gonna try to push wave as fast as possible to level 2. With your Q and W up + lethal tempo you got a really strong trading potential. You are going to use 2 AA´s on the same champ and then use a Q followed by an AA to proc your W. This deals significant damage even in early-game. In case you can proc lethal tempo before then you should be able to get in one trade 4-5 AA´s off which can take more than half HP. Keep on doing this to apply a smooth pressure on the enemies carry and supp. Always have your lane warded in tribush and a deepward in river to avoid being ganked by the enemies jungler or midlaner. For farming you want to do 2 AA´s on a minion then wait until its 1/3 hp or a bit lower and then set off 3rd AA to finish it. For canon minions i like to go safe and use a Q to empower the 3rd AA.

So you won the lane. You got more CS than the enemies ADC and maybe got some kills as well.
You now want to spread your lead to the other lanes. Do objectives, like drake or herald with your supp and/or jungler. This gives you a nice permanent lead due the dragons buffs are really strong if you stack them or get different ones (in my point of view Infernal-Mountain combo is strongest). Now you want to aim for turrets and kills. Have a good vision around the map to see if an enemy is overextending somewhere, low-hp backporting or simply out of position so you can catch him off-guard. Never go solo if you aren´t 100% sure that you can kill them without dieing. Do this over and over to take as many towers as you can and just punish the enemies for every mistakes they make.

Surprisingly it´s pretty similar to the Won side - because of vaynes strong scalings, base dmg and utility due her W she is always going to apply pressure on her main-lane and spread this pressure to the other maps. Let the enemies do what you want them to do - not the other way 'round. With enough pressure they won't get the chance to push your turrets or risk a fight without losing their own turrets. But in this case you are behind - so look for the strongest peel in your team and fight together with him to keep being safe till gettin your lead back. The most important thing is to not die. You have to stay alive - every death you got will give gold to the enemy which you could avoid by warding and by making good decisions. Vayne is a hard champ - don't underrestimate this. You will need to put time and effort into her. But if you manage to master her she gives you a lot of LP and fun in exchange.

Well keep doing like you did in Mid-Game. Use your pressure to open up inhibs. Keep a good communication with your team. This will always help you to prevent tilting or negative attitudes in your team. If the final fight breaks out use one AA on the tank. Then go in R followed by a Q once the Lethal Tempo proc is on. Your AS cap is now broken so you can delete the enemies tank or adc if he´s in range. As Vayne your focus should be Tank>ADC>Mage>Support>Offtank. So why focus the tank? Vayne has a strong impact on tanks as well because of her W percentual damage and same from BOTRK. After you won the fight just push one lane to nexus and end.

Vayne is overall a really strong champion. She glaces as an ADC or Toplaner and if it comes to take out tanks or oneshot ADC´s (i prefer playing her on Top during the Tank-Metas because you can take them totally out of them game and take full focus of the enemies jungler [you can 1v2] which gives your other lanes a big advantage). She is a lot of fun to play, it feels so satisfying to confuse the enemies with your R Q mindplays. Over all if you like ADC´s she is a must-learn because of her utility to be picked in any matchup. If you put enough time and effort into her she will become one of your favourite champions and you will win a several amount of games. If you have any questions or wishes for following guides just write it in the comments.
Best luck in the Rift
-A Stoned ADC

P.S: Check out my other Guides for Jhin and Yasuo

Yasuo:

https://www.mobafire.com/league-of-legends/build/yasuo-7-23-mid-top-total-dominaton-guide-517103
Jhin:

https://www.mobafire.com/league-of-legends/build/jhin-the-ultimate-carry-7-23-518806

If you´d like to keep up with the great support your doing for me then check out my new monster hunter world youtube channel as well, have a great day and good luck on the fields of justice :)

Link:
https://www.youtube.com/channel/UCoKCr-hcDh6K0yikPwLtxsQ