Riven is a fast-paced combo oriented champion who has great mobility and damage output. This build will allow you to use her to her full capacity and put out high amounts of damage. /this build will explain a little on how to play her. She is quick and agile but squishy as well. You need to know when to go in and when not to.

Pros
-Agile, fast character
-Deals quick, fast damage.
-Broken Wings hits all around it.
-Awesome ultimate which grants her bonus attack damage and range.
-AOE Stun
-Wind blade for finishers.

Cons
-Fragile when Valor is not maxed out
-The range of the AOE stun is very small.
-Once Broken Wings and Ki burst is on cd, she doesn't really have any abilities.
-Wind Blade is weak

I go with 21/6/3 maxing the offensive skill tree and then 6 in defense for extra armor and magic resistance. I lastly put 3 in utility in good hands so I can get back in battle sooner. I don't get perseverance because Riven has no mana so that skill would only be partially effective.

I take armor penetration marks and greater glyphs of focus for the reduced cooldowns. I get seals of resilience for increased armor that Riven needs. I take 3 armor penetration quintessences for even more armor penetration which immensely increases Riven's damage output.

I usually take Boots of Swiftness for the speed to catch my running enemies or Ionian Boots of Lucidity for the reduced cooldowns which greatly affect Riven's damage output. She is able to use all her skills more frequently. I choose to get the bloodthirster before infinity edge because it provides more ad once you maxed it out and life steal is important late game. It allows you to lane longer and do more in general. I then sell my Phage and switch it up for The Black Cleaver for that important armor reduction that it gives. It helps when the opposing team try to build armor up to counter you. I finish with Thornmail for the armor and the nice passive it provides against all AD characters.

Riven's passive increases her damage as she uses abilities. It maxes out at 3 charges with one charge being consumed upon auto-attacking.

Broken Wings is Riven's key skill. It can be activated 3 times allowing Riven to attack the enemies that the cursor is over. On the third strike, it will knock back enemies.

Ki Burst is a short aoe stun that Riven emits from her sword. The range is small but effective once you move in with Valor.

Valor is Riven's key defensive skill that protects her when times get tough. She dashes toward the player's cursor and a shield forms around her absorbing damage for a period of time. It's useful for initiating and running away.

Riven's ultimate reforges her sword granting her extended attack ranges and increased attack damage. She can then activate her ultimate again to use wind slash which is an aoe nuke that hits enemies in front of her depending on the % of health missing.

Early game your going to want to last hit more then push. Pushing leads to ganks which leads to deaths for you. You want to know your surroundings. Avoid being ganked by the opposing team.

When in team fights, I usually dive in with Valor followed by Ki burst and then my Broken Wings combo. I activate my ultimate sometime in between. Usually the beginning.

Always feel obliged to protect a running teammate from a chasing enemy by Ki bursting them and then Valoring away. Rather then letting them die.

I choose to max Broken Wings first for the most damage early game. Then Valor for the much needed health and ending with Ki Burst. Raising ki burst does not increase the duration of the stun so I find it impractical over Valor. Valor has more usefulness then Ki burst to me.

Take red buff whenever you can. It will help slow enemies so they cannot get away from you. Blue buff when you can as well, shorter cooldowns are heaven for Riven.