Umm Riven is my main champ i play Riven with those masteries,ruesn and items...i deal like tons of damage but they can't kill me.

First max your Q for better farming,when u max Q and you buy Wriggle's Latern ur farming will be soo easy.In early lvl try just to do last hit till u buy Latern.

When battle start be sure u first activate your Ulty/R then do q,hit,q,hit,q,hit,w,e-go little on side to do Ulty/R on all your enemies.
I see lot of people do all skills then activate Ulty/R...that is totaly wrong...soo be sure u activate Ulty/R then GO RAPE SOME ONE!

To help to your team go in middle battle with q,hit,qhit,q,hit and use W to stun enemies so you will give situation control to your team.