Laning as Vayne can be quite tricky as she is relatively weak early. However, what a lot of people fail to realize is Vayne's high early game damage. 3 silver bolt proc's should, at least half health your opposing ADC. So when in lane (assuming you are not against someone with a strong early game, such as caitlyn, in which case you should try your best to cs and keep the wave in your favor. If you have better all-in than your opponents try your best to not get poked down, and find an opportunity to all-in the enemy, and you should win as Vayne has brilliant all-in potential) get brush control, have your support zone (and poke a little if possible). A good way of trading as Vayne is when your opponent comes to cs, tumble and auto attack. This should make your opponent back off, if they don't you can all-in them, and assuming their support doesnt intervene, you should kill them, or come off above in the trade.

In the mid game I would focus on building a last whisper, if against taky's, or a GA if you are snowballing. Remember to keep yourself safe in a teamfight. Vayne is very position-dependent. Dont be afraid to attack a tanky bruiser, Vayne's silver bolts should take care of thier large health bar.

Vayne is one of the most flashy ADC's out there, so you can look really skillful while dominating the enemy team! Afew small things about Vayne's abilites would be, obviously, that her Q (tumble) resets her auto attack, however, her E (condemn) also does this, along with apply a proc of silver bolts. This makes you able to kill very quickly, for example, ulting then auto attacking, tumbleing, auto attacking again and then condemning into a wall to proc the silver bolts and to stun, then auto attacking again to secure the kill. Also her condemn can be used to kite, or peel. For example, pushing away a bruiser to push them out of AA range and then continue to kite them, or to push a bruiser off of you to then focus on a higher priority target, or to escape. Remember to be aware of every wall and the position of your opponent. If you can get a stun out of the condemn it's pretty much a secured kill.