I am only stating the stuff for build number 1, but most of the stuff is the same for all these builds.

Keeper of the ancient art of Wuju, Master Yi is a mystical warrior from the isle of Ionia. He descended from one of the few tribes dedicated to the preservation of Wuju, a martial art founded with the principles of absolute spiritual awareness of one's self and one's enemy. When the armies of Noxus invaded Ionia, Master Yi joined in the Ionian defense to fight the craven enemy, bringing his village honor through his unparalleled mastery of the blade. The ensuing battles ravaged the land, but no conflict inflicted as much horror as the day the armies of Noxus closed in on Yi's village. Left undefended, the village became the unfortunate test subject of the latest invention by an up-and-coming chemist, now known as Singed. The remains of the village that Master Yi returned to were so horrific that it remains a festering scar on Ionian history. To this day, no Ionian will ever publicly speak of what occurred.

After the Noxian invasion was contained, Master Yi fell into a deep isolation. For years, he trained morning to night, speaking to no one and refusing offers of consolation by fellow Ionians. The only thing stopping him from madly charging into Noxus battle lines headfirst was his pledge to keep the Wuju style alive. Even though he seethed with impatience, his rage became a tool for sharpening his practice of Wuju, developing stronger and deadlier skills for his eventual vengeance. The only thing that roused him was news of the League's formation, and Noxus's subsequent enrollment in the League. Master Yi now brings his mastery of the blade to the League of Legends with unflinching purpose: to avenge his kinfolk and end the predations of the Noxus once and for all.

This is a guide to a Ganking Master Yi.

Masters Yi's sword O=[::::::>

I have ghost and ignite for chasing enemies and hurting them. You could use Flash or Exhaust though. If you want to go complete overwhelming damage use ignite and exhaust.

Beserker Greeves: Move speed and attack speed
The Bloodthirster: Life steal and damage
Thornmail: Armor and more damage
3 Phantom Dancers: Attack speed, critical, and movement speed.

These are my items. I don't care if you don't like them. Find your own if you don't like them.

Just try to kill heroes 1 at a time and keep highlander status up for as long as possible in hero fights.

You can beat the dragon at level 14 with you ultimate. (possibly sooner) You can also solo the Baron if your level 18 and have all your items (on any build) and ignite. Make sure you use highlander and Wuju Style. Ignite is not needed just helpful.

Pros
High attack
high movement speed
critical
High Survival
can't be slowed

Cons
Weak defense early game
stuns counter ultimate

Double Strike: Master Yi strikes twice every 7th attack.

Alpha Strike: Master Yi leaps across the battlefield with blinding speed, dealing magic damage to multiple units in his path with a chance to deal bonus magic damage to minions.

Meditate: Master Yi rejuvinates his body by focus of mind, restoring health and increasing his armor and magic resistance for a short time.

Wuju Style: Master Yi becomes skilled in the art of Wuju, passively increasing the power of his physical attacks. Activating Wuju Style doubles the passive bonus damage for a short time, but the passive bonus is temporarily removed after the effect wears off.

Highlander: Master Yi moves with unparalleled agility, temporarily increasing Master Yi's movement and attack speeds as well as making him immune to all slowing effects. Additionally, killing a Champion refreshes all of Master Yi's cooldowns.

You want to use alpha strike to catch your target then use E and R to gain super damage. You can also use ghost and ignite to get in more damage.

Use Alpha Strike on minions to get gold and to fill the boost for The Bloodthirster. Then of course last hit everything. Also if you have a Bloodthirster and you guys are pushing then you should run into the jungle to fill them.

Wuju Style is very strong early for last hitting minions.
 
Try using Alpha Strike on a minion in front of an enemy champion so you are placed at a safe distance at the end of the spell.

On all these builds if you get all the items then get a Phantom Dancer in place of your boots.

This is for ganking. Enjoy! :) This guide is very simple but effective.

You'll know if you did good if you have at least 10 kills by the end of the game. My record game was 21/1/5 it was awesome.