I've only played her against bots, but I've been going Attack speed first.
Health potions and boots to start, and additional potions as necessary.
AS Boots, then a Vampiric Scepter for sustain.
I move into a Phantom Dancer.
Then a BF sword to either continue a Bloodthirster, or start an Infinity Edge.
Most of the time I don't get the Infinity Edge built.
The attack speed from the Phantom Dancer helps with kill securing, and the critical makes it actually hurt; not to mention that you can now roll through a group of minions.
What I find is that I have to chip away at enemies at first, especially the bruisers.
Generally, hit, hit, Q, hit for true damage, back off.
Unless I catch them between me and a wall, and then they definitely get an E.
Once I get the Phantom Dancer, the kills start coming faster and faster.
So to me it seems that Vayne peeks later than many champions.
But that's my opinion.
I'll try getting some attack damage first and see if it makes a difference.