Master Yi is often considered an easy champion. Pop steroids and right-click. The problem is that he is too squishy to just charge into a fight. He needs too much gold for his items to be of use. He has no cc of any kind. So regardless of what people think, Master Yi isn't the ezmode champ people make him out to be. That's not to say he isn't good. Master Yi, when fed and farmed, can wreck teams completely with his Highlander and it's ability to refresh cooldowns. If you want a carry that can destroy everything in it's path after 40 minutes of farming, Yi is for you.

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' 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.

''The art of Wuju lives on in Master Yi, and is plunged through the hearts of his foes.'' -- Soraka, the Starchild

Pretty standard jungle runes.
Greater Mark of Desolation for the great armor pen.
Greater Seal of Armor to help jungle and take less damage.
Greater Glyph of Attack Speed to jungle even faster.
Greater Quintessence of Desloation combined with the ArP marks for MAX ArP.

21/0/9 to get a ton of dps and the 9 in utility for faster EXP and longer buffs.

Cloth Armor + 5 Health Potion
Wriggle's Lantern
Mercury's Treads
Infinity Edge
Phantom Dancer
Phage
Bloodthirster
Last Whisper
Black Cleaver
Frozen Mallet
Cloth Armor + 5 Health Potion will let you jungle for a while. You should be able to get a Madred's Razor and Boots or a Wriggle's after a while. After Wriggle's, getting boots is important. While I like to make out that boots are always situational, Mercury's Treads will almost always be taken. Simply because the 35 Tenacity is to good on Yi who gets countered so hard by CC. Afterwards work on the Infinity Edge + Phantom Dancer to give HUGE DPS. A Phage is taken next for the perma slow [25% chance to slow at 2+ attacks per second? Hell Yea!]. We get BloodThirster for more AD and a stat we crave LIFESTEAL. With this baby we can backdoor like a boss, win any 1v1 [or1v2] and just be Master Yi. AFterwards it becomes situational. At this point if you have all these items they hsould be stacking armor, in which Last Whisper would be SO Helpful. If they aren't get a Black Cleaver. Finally finish into a Frozen Mallet for that tru perma slow and the extra health always helps.

Smite
A Must have for any jungler
Flash
Just an exception summoner spell. Probably the best in the game.
There aren't really any other summoners that you can use.

Alpha Strike
Used as a gap closer, chasing ability and for a faster jungle. It can also be used to partially block cc and skill shots.
Meditate
Heals you. Quite useless. Don't get it until the end.
Wuju Style
Passively increases your AD and can be activated to double the passive. Really good.
Highlander
What makes Yi be Yi. Cancels all slows, increases Movement Speed and Attack Speed GREATLY. The best part? If you kill someone ALL skills cooldown are refreshed! You can also use Wuju Style and have both the Passive and the Active. Epic :o

Skill Order
Highlander> Alpha Strike> Wuju Style> Meditate
Alternate between Alpha Strike and Wuju Style, picking up Highlander whenever possible. Leave Meditate til the end.

Here is the video of the jungle route by stonewall008: Play Video The path is:
Golems > Wraiths > Wolves > Blue
Golems > Red > Wraiths > Gank

As Master Yi, you are expected to farm and push 24/7. Farm, farm, farm. Your items are expensive! After you get a few of your items towers drop in seconds. Master Yi is one of the best pushers/back doorers in the game. Use this. Master Yi should really be in teamfight until he finishes most his items. When teamfights happen [and you don't have your items yet] just push a lane and hopefully get a tower. Once you finish your BloodThirster, then you can start destroying Teamfights.

You are squishy as hell. Be careful. Come in at the right time, when their cc is gone, and then Highlander Wuju Style and right click to victory. I can't stress the importance that you are SQUISHY and will die really fast if you get focused.

Master Yi needs farm. He needs gold. When he gets the farm to finish most of his build, he becomes unbelievably strong. He takes down towers very fast, split pushes like a boss, and is really strong 1v1. With his full build, he can carry his whole team.