Hey, i tried out vayne and AMAZING CHAMP...
to start, i chose to get alot of atk speed and sum dmg

i chose to start with dorans for the dmg and lifesteal. after get sheen because this is going to b a main part of harass. i get shoes for the atk speed and speed. after i get trin force for the extra dmg and the effect thing. from here get a dancer for massive atk speed boost and critical chance. then i get starks for lifesteal which will help you alot. after u need sum dmg so i get cleaver for both dmg and atk speed AND armor pen. from here, you can get a madred, or if they have a jax get a sword of divine. if you feel that their more on the hp ***** side, get inf edge for dmg.

i get the armor pen for that extra dmg. also the cd reduc for more spam of tumble and then mp regen so u dont mana starve

i went 21-0-9. 21 because vayne is more of a dmg not a tank or caster. i got 9 into the end for the exp boost, gold, and ghost. and some mana regen

for the skills i would suggest starting off getting tumble first. then add 1 to silver bolt and then another to condem. this will help in harassing. afterwards, i just max tumble and silver bolt cuz their the best to use. i dont usually use condem idk why... but i use only for the stun mainly.

What you want to do is HARASS LIKE HELLLLLL... if you mid, hit them, tumble, then hit again. that will deal to the least 300 dmg at around lvl 8. and if they over extend near you, hit tumble between them and the turret, then push them away from turret, atk again, tumble, then keep atking. also, if you have ult, use ult b4 goign in.
For the best harass, hit once, tumble in for another hit then push away. this will cause the 3 silver bolts, the dmg from push, and tumble dmg. major harass and escape if they charge u cuz u can push.