Well you could start with telling us what your setup is. I personally run Conqueror, Triumph, Tenacity, and Coup de Grace as my primary runes. For secondary Riven could use anything really. You could go Inspiration and get the extra 5% cd cap and another inspiration rune. I run Shield Bash and Overgrowth under Resolve to give Riven a bit more durability and power during in engaging. You could also go Domination and run any of the first three runes and Eyeballs. Even Sorcery could be interesting if you take Absolute Focus(to increase your Q dmg) and Scorch.
As for items you should always start Long Sword and three health potions. I build a Tiamat first however to help with the farming like most melee tops do. As for what complete item you should be get done first definitely Black Cleaver or if you want more dueling power Spear of Shojin(though I highly recommend this only if Laning Phase is going to last longer than usual as you should still build Black Cleaver afterwards). If you go Cleaver first you should be getting Death's Dance next and getting a Boots of Lucidity to complete your 40% cd(or 45% if you took the Inspiration runes). After those three items you'll need to either finish that early Tiamat or sell it but getting Titanic Hydra will give you a lot of AD and Health making you a bit more durable. After that it really depends on what the current state of the game is and how well you can play. If you're getting burst down before you can engage or you simply can't engage cause the enemy has too much dmg Guardian Angel(for the Stopwatch) and/or Mercurial Scimitar(for the QSS if you're getting hard CCed). If you're barely even taking dmg or are avoiding the CC Guardian Angel is still recommended but if not I build Sterak's Gage and Bloodthrister to give me more shields, health, and life steal.
If you're already building Riven like this then it's just your play style. It'll just take constant practice learning how to farm in lane against any champ, how to engage and all in, when to roam, when to reset, ect. Riven excels best at punishing opponents that auto a minion as you can E-W-AA and Q away or if you think you can out trade Q-AA-Q-Q-AA will do a ton of dmg but you'll have to commit to the fight then. Or you can land a third Q-W and E away for another hit-and-run strat. If you can't trade evenly then using your Qs to last hit minions and E away to get what you can is what I do. Sometimes I can just walk up and AA a couple in some matchups before they start chasing me. Farming under tower as Riv is very easy once you got Rank 4 Q as it'll always kill casters with 3 Qs and always 2 Qs at Rank 5. Melee minions is always to get with empowered Autos if your minions are atttacking it with the tower.
