Welcome to my first build, first of all, I must say I'm not a high elo who makes guides, I'm simply a player (1400 elo) who knows about the game. So, reading about my guide might help you if you are a beginner in this game, and will allow you to dominate most games as Ad carry, without counting the ingame factors (Junglers, supports, etc).

This guide will only help you have a main idea about how to build vayne, not really much about farming or how to position yourself.

The runes I use are the ones that are in both builds, but the Marks are exchangable with Attack Speed to have synergy with AS Vayne build. The rest of runes must be the ones that are there to be able to withstand the lane and try to dominate.

Not much to comment, usual 21/9/0 with the difference of using the heal mastery or not in the Defense part.

You are an AD Carry after all, meaning you need that high damage to make as much damage to the enemy team. Starting with boots and 3 pots means higher sustain in lane, but if you have a healing support, you can always use a Doran blade to maximize damage early. After that, just follow the build you want, but remember, items are always situational, meaning, if the enemy team has a lot of armor, it's better to build a Last Whisper in exchange of Black Cleaver to make heavier damage against armored tanks.

I prefer going with R>W>E>Q, and that's because the damage difference between leveling each skill is different. When you level up W first, the damage you make is clearly higher when you compare it with the Q, because Q is a % of your total AD, and early game you won't have as much damage as you will in late game.

Flash is a must, the other spells you can use:
Exhaust
Ignite
Heal
Cleanse

All of this spells except ignite, can help you escape from difficult situations, since your escaping methods aren't as good as other champions.

To learn how to farm and position yourself, watch videos in youtube. Remember, this build will only help you know how to start with vayne, not really much what you do ingame.