On the beggining you should lane with someone that can give you health and protection such as alistar or taric and the statikk shiv gives you an early burst of dmg while creeping so play defensively early game.When you get your ulti you can start playing as much offensively as you can and try to dodge anything with your timble, so first activate ulti then wait for a skillshot do dodge(such as Ezreal or Corki have).Mid game you will need to have some critical damage as well as life steal.Consider that your ultimate gives you attack damage so you will not be needing to build a lot of damage in early and mid game and also your passsive and silver bolts give you damage.It would be better to build attack speed and critical on the beggining, but in the late game you should be having items such as frozen mallet for extra slow, infinity edge,bloodthirster statikk shiv,blade of the ruined king etc...All in all vayne can easily get fed if you play defensively because of her insane damage that her passive gives her combining with her silver bolts and ultimate ability.