on vayne i use:
marks with flat attack speed/damage
seal with flat armor
glyph with flat magic resist/ magic resist per lvl/ flat attack damage
quintessence with flat attack damage

When vayne is lvl 1 dont try to go play agressif, her power is verry low in the begin game.
I recomment to farm till lvl 6, that's around 10 min normaly.
After 10 min ingame, you try to have at leat 80 minion farm or more.
Tip: In begingame dont try to farm under your turret, the damage is not high so you will lose allot of minions.

In begin game, try to stay behind your minions and ask your support for help. Ask if he can stun the other ad carry allot, so that you can do your 3 basic attacks for a silverbolt effect.

Dont try to solo in endgame, your health is rather low and the other team will kill you.
Try to stay on the background in teamfights, seek out easy targets (ap/ad carry) and focus the tanks afterwards. Then the pentakills will folow up shortly.