I started to play Vayne and think she was an epic champion with hers true damage she give, and have made a little build there make hers true damage hurt a lot.
With this build you should go, i prefer to do it, and try to last hit so many minion as posible if you do it well you will go gank before lvl 6, and if got push by you opponent you will need to wait a little longer. you need to gank and get some kills or assist this build will take you long time get full build

I have get that experience that you should make true damage faster and when you not make that armor penetration will be nessecary for a fast kill specilly if thay are tanks so that is why have chosen this runes

- Glyph, Greater Glyph of Alacrity, 0,64% attack speed = 5,76%
- Seal, Greater Seal of Alacrity, 0,76% attack speed = 6,84%
- Marks, Greater Mark of Desolation, 1,66 armor penetration = 14,94
- Quintessence, Greater Quintessence of Desolation, 3,33 armor penetration = 9,99

i have chose to make 21-0-9, cause she is need masteries there give here more attack skills so she will could kill her enemy faster, and utility masteries for some mana regen and some more gold that gold always is a good thing to get fed faster.

To start with get ait will give you some life steal, make you be in lane a little bit longer, some health you not will be more difficult to kill you 1v1, and some damage there will give you a chance to get first blood.
next go forit give you some attack speed, like i have written before ataack speed is important to get true damage fast.
and now you should get ato get some more life steal so you will could heal you self by attacking minions and you will be more dificult to kill in a battle.
So its time to hurt, you should getthen it give you both damage and attack speed, when you have it time to upgrade yourto aand get one more so will you have a crazy damage and almost 50% life steal if you have full use of bothand the last item you should get is.
If you have this 6 item you chance yourto ait will give you a higher crit chance, attack speed and a increased movement speed and it will make infinty edge more valuable.

i have chose flash so if they try to gank you in mid, it will be easier to escape, it also usefull if you are in forest and get gank jump over walls ore something it will make it easier to get away from battles you dont have a chance in but it will not happen if you follow my build ;)
i have also chosed ignite so will it not be able to get from you with low hp.