Hello everyone, I will try to teach you all i know about Yasuo, my main.
Read all notes, they give vital information.
Sorry for my bad english ^^

Start with a Health Potion and Doran's Blade, build Statikk Shiv first, then chose between Berserker's Greaves and Mercury's Treads, pick Mercury's Treads just if you are having problems against AP.
If you are fed I recommend you to rush into Infinity Edge, to snowball hard, if you are not fed, build Trinity Force.
Then go to Bloodthirster and Ravenous Hydra

When facing ranged go for a very agressive start. Remember to keep this ability stacked, farm with it if necessary.
When facing melee evolve and attack them when they come to farm

- Best spell in the game, when ganked, use E on the jungler then flash away.
- Good spell for laning phase. Remember! you can use it during your ult.

In a teamfight, use your to protect everyone, try to ult soon, or other champ that sends enemies air can help a lot.

-When i play , i try to go very agressive, you can always ask to your jungler if he can ward for you.
-If the enemy don't have projectiles, your can be very usefull, use your Wind Wall then your Tornado very fast, the tornado animation will disappear and probably the enemy will not avoid the tornado.
-A easy way to pick a kill is when your enemy is under tower, hit your tornado, ult and when ulting. easy tower dive.
- can be used when uses but you must react very fast.

Yasuo is a very funny and easy champion to play, but very hard to master and play properly, i hope you enjoyed and learned something with this guide.
Remember, everything in this guide is MY opinion.