Masteries
My preferred masteries on Riven is 11/18/1 being that 21 in offense does not benefit her much due to her very weak early game damage and general squishiness. Riven is much more of a mid and late game champion, which can be hard to get to without some early beefy stats.
Runes
My runes maximize her mid-game damage while also buffs her early game lane squishiness. This allows you to survive your rather weak early game and still assists you in mid and late game.