Hello Everyone, I am a good Yasuo player and want to show you my guide because i think i can help you.
For the first at all, You need only a boots because Statikk Shiv is very important for harassing.
Sheen gives Ability Power that fits for E, but its Spellblade even gives bonus Damage to Q, that can increase your damage output, and even burstout.
Try to focus on farming, not on kills. Only go kill if there is a jungler that helps you, and the kill is totally secured. I recommend getting Infinity Edge, because it gives Yasuo a total of 50% critical because of his passive doubles his Critical Chance, with Statikk Shiv up to 90%. Last Whisper is one of the most important item for Yasuo, gives him 35% armor penetration, that means much against tanks, even against offtanks. Try to focus out the AP carry, and the AD carry with Yasuo, you can even start farming at the jungle to stack your Q up for the Airborne.
This helps you to kill earlier the AD or AP carry.

For Quintessence: Only 2.25 + AD 3x
Glyphs: Magic Resist 1.34 9x
Seals: 1.41 Armor 9x
Marks: 0.95 Attack Damage 9x

OFFENSE
Fury 4x
Brute Force 3x
Expose Weakness 1x
Martial Mastery 1x
Executioner 3x
Warlord 3x
Spell Weawing 1x
Blade Weawing 1x
Frenzy 1x
Devastating Strikes 3x
Havoc 1x
DEFENSE
Recovery 2x
Enchanced Armor 2x
UTILITY
Phasewalker 1x
Fleet Of Foot 3x