Start only Last-Hitting the minions
After 1st kill or vampiric can be more agressive, poke with Q+basic.
After Blade is easy to farm, remember Vayne is a late game champ

Remember the combos:
basic+Q+basic:detonate passive and deal a lot of dmg
basic+e+basic: detonate passive and stab, can stab for run witouth the basics.
try keep the bot bush warded, so u can stab the supp everytime he come into it.
Remember use the active ob Blade (BOTRK)
Tumble Reset ur basic.
While u are using your ultimate can be useful spam Q for not being targeted in a tf.

Keep the bushes warded.
Vayne is the best adc on late game, never run out of a 1v1 fight, u have dmg, lifesteal and ways to run.
try focus, if u cant, attack the closest enemy, u can kill tanks easy ty of your passive of silver volts and the BOTRK
Get objetives faster u can, can rush BOTRK and phantom fast.

pros:
best late game adc
easy to run
can kill tanks easy
grat movement thanks to Q and ult
E allows u to keep distance of an enemy focus on you
if nobody focus u, u can carry an entire team.
cons:
one of the worst adc on early game
can easy get oom in a large fight
oracle delete ur ult+Q
early ganks can cost u the game if u cant farm after that.
vulnerable to aspd disables and cc. (stuns and aspd slows like Nasus)
Too squishy