Yasuo is High Mobility, High Damage Fighter and Assassin who excels both in Team Fights and Cat Fights. Yasuo is hard to use at first, but an when played by an experienced player, can be really deadly.

Your Runes focus around Crit Chance and Crit Damage, taking advantage of his Passive Ability. The Armor and Magic Resist is just for Durability. The Armor Penetration Marks, Last Whisper and Last Breath Armor Penetration Bonus are for MASSIVE Penetration.

The masteries focus on Attack Speed, Cooldown Reduction and Attack Damage, well because Yasuo needs those things. He needs to deal a lot of Damage while also lasting long in a Team Fight.

The items, just stick to the Core Items above and just add situational items depending on how the game goes.

Prioritize his Q and E. Of course, getting your ultimate at available levels. Simple: Q<E<W

Usually, I take Flash and Ignite, if I want to play it safe, I get Flash and Barrier.

Pros:

+High Mobility
+Can chase effectively if done right
+Can block ANY Projectile
+Harmonica/Flute skills
+Can kill fast while being a bit durable
+Can speak in Japanese and Ancient Ionian
+Is very useful in Team Fights

Cons:

-Very squishy Early to Mid Game
-Weak Pre-6
-No snowball = Very weak
-3rd Q missed + No Knock-up in team = No Ult
-Needs to Cast Q three times and land a skillshot in order to use Ultimate without Knock-ups
-I don't understand Japanese or Ancient Ionian

Use your Q at level 1. At level 2, it would be easier to use your E, since Q still has a long cooldown at these stages of the game. Once you get a Statikk Shiv, one Q = half a minion wave.

1. Harass Combo (Can be done Pre-6): E-Q-E
-Get a full flow bar.
-Dash through a minion to get to the lane opponent in range for a Q.
-Use your Q on the lane opponent.
-Dash back to safety through another minion.
2. Kill Combo (Can only be done after level 6): Q-Q-EQ-R
-Get a full flow bar.
-Use your Q on a minion.
-Use your Q another time, for a second stack of Gathering Storm.
-Dash through a minion and use your third Q mid dash to knock up the lane opponent.
-Use your Ultimate.
-Follow up with an E-Q Combo to clean up if the enemy is still alive.