Hello everyone. Well, first let me say that I am not a veteran in English, not American and I know just a little. I am currently using Google Translate. And I would also say that is the first guide that I do in my life. So I hope you enjoy and understand. :)

Riven is Melee/Fighter. Very good for ganks and fights hand-to-body. At the beginning of the game can be a big nightmare for your opponent, if you can get your farmer and Ionian Boots of Lucidity quickly.

-Pros
-Using Valor, Broken Wings and Youmuu's Ghostblade, Riven can easily escape from their enemies.
-Great damage, in early game. If feed, can easily pick some doubles or triple kills. If you're lucky, quadra kill, maybe penta. So good lucky.
-Ignite can't kill you in almost times.
-Stun in area.
-Ultimate can be annoying to your enemies.

-Cons
-Silence can be deadly.
-Shortly HP early game.
-High CD early game.
-Her weakness is the CC.

Well, my build may seem strange, but works very well for Riven.
Starting the game, my first choice is not another: Doran's Blade is the first thing I do after stepping on Summoner's Rift. Then you have more than 350 G, I buy Boots of Speed. ​​If you're being focused, two or three potions. Then I finish Ionian Boots of Lucidity.
After it ends, I buy two Long Swords, thus increasing my AD to raise money for The Brutalizer. Finishing The Brutalizer, I usually add 1350 G and finalize Youmuu's Ghostblade, if I am able to kill enemies easily. If I am not able to kill some enemies, I buy Averic Blade, then soon after, Finishing Youmuu's Ghostblade.
Your Youmuu's Ghostblade should be put to good use in 1v1 battles or TFs.
Youmuu's Ghostblade not do very well at the beginning of TFs, but can be of great help.
Can be used also for pursuing enemies, or running away from pursuers.
After finishing Youmuu Ghostblade's, I start buying Ruby Crystal, if the money is greater than 1315 G, I buy Phage, but if money is not enough to Phage, I buy Ruby Crystal and Long Sword, soon after, ending Phage.
When Phage is ready, try to do some Ganks on enemies who are farming alone in lanes. If the opposing team is together, try to win 1 or 2 TFs, maybe getting money for Giant's Belt.
If you are unable to kill enemies, kill some monsters in the jungle. When you get enough money, finish Frozen Mallet.
If you think you have low armor, start your Atma's Impaler by Chain Vest. If you think that your armor is enough, start by Cloak of Agility.
Ending Atma's Impaler, earn money for your next Giant's Belt.
Start your Warmog's Armor by Giant's Belt, sell your Doran's Blade and buy Ruby Crystal. Earn money and complete your Warmog's Armor.
Your build is almost complete, will now depend of the match and your point of view. If you want a few more kills, get your Infinity Edge by B.F. Sword. But if the opposing team is much AP, make a Banshee's Veil, starting with Negatron Cloak.

Well, let's get right to the "subject". If you want an aggressive Riven, start maximizing your Ki Burst, and then Valor, and finally Broken Wings. If you want a defensive Riven, start maximizing Valor, and then later Ki Burst Broken Wings.

P.S: I'm sorry for the little guide, I have no experience guides and tried to do my best. :( But I hope you understand. Thank you.