In the begining i want to say that this build is made on my own experience. Maybe someone find better way to make fun with playing Riven. Its mine way and i hope you will like it.

I use runes for atack speed. Actually i have universal runes for few champion. I use it and its good for the early game. You will have better start with last hiting minions and fight on line vs opponents.
Second runes which i used are armor penetration. Its great, because you need strike enemies whose have some armor, and you will deal more damage to minions.

Like you see masteries are 21/0/9. I used them for fast farming cash and level. It will get you adventage in early and mid game, and of course in late at least.

Its good increase Q at first. It has a lot of dmg and remember that you must use it with your pasive.

For example:
First use Q and hit
Second use Q and hit
Thirth use Q and hit

Q is good not only in fight. You can use it for fast run away from dangerous places.

Second skill which i prefer to increase is W. Its your stun and you need to learn when you should use it. I like use it when someone try to get out of my combo or when my ally has trouble i try to fast stun all opponents whose try to kill him.

Last skill i increase is of course W, because ulti you need increase when you can.

And now i will say "why i used such items on Riven".
First Doran Blade. Its good for the begining. Next i try to get cash for fast Rejuvenation Bead and basic boots. Why i like this item? Its cheap and i can use it later to make Randuin's Omen. It gives you nice hp regen for not much cash at the begining of game.
Next what i buy is Warden's Mail and Mercury's Treads. At this time for "paper champions" this boots are best contra for crowd control effects. Next i buy fast Wriggle's Lantern and i end Trinity Force.
Two last items its for you own choose and look at opponents champions, what you need to be more deadly for them. I prefer The Black Cleaver and Madred's Bloodrazor. They are good vs tanks and not bad vs others, but if you think that something else will be quite better - just buy it ;]