Yasuo is a Hyper AD Caster with a slow build-up to late game potential. Yasuo's kit allows skilled players to rush on top of their opponents by using minions and/or neutral monsters to close gaps then pounce on opponents with huge critical chance. I'll try to keep this guide as simple and short as possible.

I take flat armor and magic resist seals and glyphs respectfully so I can withstand damage early and worry about itemizing my opponents later. I utilize my marks and quints for late game potential as this is when plays become more crucial to winning. Any combination of Atk-Spd/Lifesteal/Atk-Dmg greatly improves his chance of success but I lean more towards late game than early and rely more heavily on my jungler for clean up potential in the pre-6 stage of the game.

Masteries are pretty standard for AD casters, except for cooldown reduction (CDR). His Q scales with Atk-Spd so CDR is pointless.

Optimal Build path is:

Berserker Boots (Furor)
-Not crucial can be swapped for merc treads to slow down CC

Infinity Edge
-Main Item for Yasuo ALWAYS BUILD THIS
-Increases damage Greatly

Phantom Dancer
-With IE crit is now 100%
-Easier escapes (movement through units)
-faster movement spd (stacks passive faster)
-Increased Atk-Spd (stacks Q faster)

Blade Of The Ruined King/Bloodthirster
-BOTRK for HP heavy teams
-BT for squishy opposition
-I usually build both as they stack quite well

Last Whisper
-Armor penetration it's good for you bad for them

If my team is behind I might build a defensive item to survive during teamfights
-Randuins Omen (Heavy AD Team)
-Spirit Visage (Heavy AP Team)
-Warmogs (Double Assasins W/O BOTRK)
-Mercurial Scimitar (QSS Passive)

I considered Youmou's Ghostblade, Ravenous Hydra, Trinity Force, Statikk Shiv but his Q allows on hit effects like lifesteal/crit/movement spd so your survivability comes from spamming Q and hitting multiple targets and procing all that lifesteal.

Max Q this is your main source of damage besides AA
Then E so the CD reduces as you level allowing chasing to become easier.
Take a point of W at lvl 4 so you can block ranged skills/Auto attacks.
Ultimate... Kinda want that... Maybe....

Flash Ignite or Exhaust

Flash - Escapes.

Ignite - Better follow up on ganks or dives/Better Snowballing

Exhaust - More defensive/Better late game

Pros
-Huge late game potential
-Massive damage and CC on ULT
-Shield when attacked reducing followup damage greatly
-Huge Ult Range
-Fast Atk-Spd/Movement
-Double Critical Chance
-Blocks a huge set of skills with windwall
-Samurai.

Cons
-No real escape
-Slow early game
-Hard to follow up on ganks without CC
-Item Dependant
-Dash damage falls off late game
-High skill level
-Ult has very short window

Try to get a team with knockups:

Janna
Malphite
Nautilus
Wukong
Jarvan IV
Lee Sin
Lulu
Riven
Nami
Vi
Sejuani
Xin Zhao
Zac
Zyra

I want to talk about Windwall - The W

Windwall blocks all projectiles except for towers.
That means anything with a forward motion.
Ranged auto attacks.
Ashe's Crystal arrow, Zeds shadow, Lux/Ezreal Ult, Wukong dash, Blitzgrab...
ANY PROJECTILE CAN BE STOPPED WITH WINDWALL.
You can use this skill to prevent poke when you go for CS. (great against Oriana)
Timing is crucial.
And remember that the wall creeps slowly forward so not get caught thinking your safe.

E-> Q

Dash to champion -> AOE Spin that Crits

E-> E-> Q

Dash to minion -> Dash to champion -> AOE damage
You can dash to as many DIFFERENT ENEMIES before hitting enemy champions.

Q-> Q-> Q-> R-> E-> Q

This is the ranged/lane combo.
Charge up the knock up, activate it, then ult and clean up with an appropriately timed dash and an AOE Q.

Q-> Q-> E-> Q-> R-> Q

You can combine this combo with the one above to close the gap on enemies.
This is the teamfight combo, charge up your blade, knock up your opponents then ultimate.
Follow up with more Damage.