FARMING (Trust me you want to farm a lot)
Last hitting minions is massively important to gaining an advantage over your lane opponent being up by just 30 cs is nearly equivalent gold-wise to being up two kills. This kind of advantage directly translates to your ability to snowball the lane, and ultimately the game.
You should be farming as much as possible, but sometimes it might not be that way.If that's the case, you have to have patience until late game. Play Video Ok so Vayne's Auto + Thumble is definitely weaker than a Draven's auto attack while Q is on or even worse if he has 2 Q on.The best thing for trading in lane is to try your best to trade for 3 auto attacks. This way when you are maxing [W] you will definitely come out ahead as long as you can proc silver bolts.If u have 80%+ mana its not bad to do Q+AutoAttack+E to proc silver bolt. Just remember condemn costs a lot of mana and has a high cooldown so think before trading that way.Good way to keep on top of your lane is if you have a support that iss not passive (example: Thresh/Alistar/Blitz and not like a janna/sona) then if you see the enemy support out of position, you can use your condemn to knock them against the wall and set up a CC from your support, leading for a possible kill. Constantly look for plays so that your opponent bot lane won't be able to think they can just take advantage of you. You have to show them that you're good! At level 6 you can win against most of ADC's, as long as you can make good use of your final hour. If your support has a CC ability and they use it right, you can pop your ult right away and look for a kill. Even if you don't get a kill, don't worry you probably came out on top and your ultimate has a relatively low
cooldown. You have to be careful with enemy laner if they have more items than you ( if you come back with a vamp scepter, and he with BF sword) and you have to just try your best to pull the creep wave near your tower and last hit under tower. If you're able to last hit under tower calmly, you should be completely fine. If anything,if you get your outer turret destroyed early freeze the wave IMMEDIATELY (which means you last hit at the very last moment) so that the enemy bot lane HAS to overextend to continue farming from bot lane. If you're able to do this, you should be completely set with catching up! You need to be very patient with yourself when learning how to team fight. It's not easy you can't win any games if you don't team fight well.The mid game is all about getting to the late game as fast as possible. That means taking dragon or baron,farming lanes as much as possible and team fighting once you have two good items. Your job as adc especially as Vayne is to wait for the teamfight to start and destroy the enemies frontline as much u can. Mostly attack the closest targets and try to finish someone off before switching the target FOCUS on one target. So better pick up the right focus and get your Silver Bolts doing the rest.For using your ult recommend popping it as soon as possible to deal as much damage and pressure as possible at the break of the fight.Your mechanics and positioning with Tumble [Q] will be important here.
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Night Hunter (Passive): Vayne gains visible 30 bonus movement speed when moving towards a nearby enemy champion. FINAL HOUR: Night Hunter's bonus movement speed is tripled to 90.

Tumble (Q): Vayne dashes in the target direction, though not through terrain, and her next basic attack within 7 seconds deals bonus physical damage. Tumble resets Vayne's basic attack timer.

Silver Bolts(W): Vayne's basic attacks on-hit and Condemn apply a stack of Silver Bolts for 3.5 seconds, stacking up to 3 times, with the duration refreshing on subsequent applications. Applying a stack to a different enemy removes all stacks from the previous target. The third stack consumes them all to deal bonus true damage, with a minimum threshold, and capped at 200 against monsters.

Condemn(E): Vayne fires a heavy bolt at the target enemy that upon arrival deals them physical damage and knocks them back 475 units, though not through terrain. If the target collides with terrain, they take bonus physical damage and become stunned for 1.5 seconds.

Final Hour(R): Vayne equips her crossbow, gaining bonus attack damage and tripling Night Hunter's bonus for a duration. Additionally, Tumble's cooldown is reduced, and casting it grants Vayne invisibility for 1 second. Attacking or casting Condemn breaks the stealth immediately. While active, scoring a takedown against an enemy champion within 3 seconds of damaging them extends Final Hour's duration by 4 seconds, up to its original duration.

Always take flash.

Most of the time or if you are not familiar with other summoner spells you can go with Flash+Heal combo its the most used combination for a long time.

Cleanse is mostly situational, you should take it when you are facing heavy cc like or

Exhaust can be very powerful and will allow you to survive burst damage from assassins but also in early laning phase, it reduces damage taken and can help you win early fights. Also since we are playing vayne with exhaust we have advantage in 1v1 scenarios.