Riven is really weak in early lanning phase because she's an Assassin fighting (most of the time) huge tanks.
But thanks to the new ferver battle mastery you can now have a great early game and be a good frontline for lategame.
Go for x9 lethality marks ; x3 AD flat Quints ; x9 flat Armor seals ; x9 MR per lvl glyphs
Lethality is not so great in early game, but because you'll stuff without any armor pen you must have this for lategame in order to OS squishies in teamfights.
Go for 18 0 12
Take as most damage and lifesteal as possible in masteries(depending on your playstyle).
Make sure you take ferver of battle.
Blade + pot starter
=> Kindlegem for health and cdr
=> Jaurim's Fist for health and damage
=> black cleaver
=> Spirit visage
=> death dance
Against full ap u'll took malmortius instead of death dance
Against full ad u'll take warmog instead of spirit visage
How to play ?
If you play against squishies (gp, jayce, yasuo,teemo...) took damage right after kindlegem (as tiamat for example) but vs tanks and counters (renekton, irelia, maokai, malphite) take as much health and tankiness as u can in earlygame.
Thanks to the new mastery u'll still have damage (20 ad at lvl 6) and that will be enough with Jaurim's Fist to win trades and all-in.
In lategame, wait for a flash combo in their backline, with a full combo (nidalee jr/the shy) u'll be able to OS them if u don't get exhausted and then peel for your team, u'll have a great amount of damage and you'll be execivly tanky for a riven. They will try to kill u but if they don't over focus you they won't be able to do so.