Vayne is one of the strongest ad carries ever made. She is very good in taking out single targets and her DPS is pretty high from lvl 1-18. The biggest pro is that she is very mobile and this is why people fear her!

Red - Armor Penetration - a sure thing for every ad carry
Yellow - Attack Speed -some AS is always good for Vayne
Blue - MR - good against casters
Quint - 2 Flat Damage and 1 Armor Penetration - gives me the necessary damage which I need in the early game

3/6/21 is a good masterie build because it gives me some major staying power in early game against strong burst damage and the 21 points into utility gives me shorter cooldowns on my skills and the summoners spells. Also I have enough mana reg which gives me the ability to spam my skills to harass enemy or to farm and Vaynes early dmg is pretty high thats why I m not using 21/0/9 masteries build.

But the 21/0/9 masteries build is also a good one!

I m starting with the boots of speed and 3 heal potion because I can use Vaynes mobility better and through the potions I can stay longer at the lane! The two doran blades are giving me staying power and some good early dmg.

Now if the enemy team has some major cc and burst dmg I would prefer to buy banshees after my 2 doran blades and the berserkers boots. It gives me the staying power which I need against the enemy.

The listed ad items should be bought by every ad carry especially the infinity edge!

Flash should be always a sure pick for any carry because it will save you always when you get ganked or in other situations.

It is possible to take ghost as the second summoner spell but I prefer exhaust because with this spell I can take down single tragets easily and this is Vaynes job!

Vayne is a pretty strong ad carry because of her mobility and her early game dmg output which gets higher and higher. Because of her high early game dmg you can easily harass your enemy and farm him out. Until 6 you should dominate the lane and since you are level 6 you can easly kill your enemy. Once you have this early game advantage you should use your benefit wisely when the game extends!

Sry for my English, I know it is not that well.... Thank you and gl with this guide/build!