Ok, I like you, used to get completely fucked by Riven. Things to do, TRY to pick Darius(strong early/good poke), or someone like Irelia(safe with stun, lategame SUPER tank). Also, the absolute best way to kill Riven is, camp her, and camp her hard. If she dies 2-3 times within the first 15 min of the game(of course without her TPing and getting kills) she won't come back. She needs to snowball, and is a master of feast or famine. Let me put it this way, smart people build tank when behind, and Riven's abilities are some of the hardest AD scaling abilities in the game. So if you put her behind, she will be building tanky(if not then you smash her like a fly) and her abilities won't scale(her shield will be absolutely meaningless).