A very strong duelist , master yi can clear the jungle very fast . The jungle will provide him enough money , or even more to keep up with the rest of the team . His ganks are not the best ones , and you can consider getting exhaust instead ghost summoner spells.

+Very strong duelist
+Good in teamfight
+Very good assasin
+Can soak up good amounts of dmg using Meditate
+Has true damage ,no need for armor penetration
+Aplha strike can crit.
-Squishy when Meditate is down
-Focused
-Bad early due to attack speed problems
-Countered by blinds or stuns
-Mana problems
-33 seconds cooldown on meditate

Master yi is a full ad champion jungler assasin , so consider getting for runes some durability and ad , for masteries get all ad and attack speed that exist and a little movement speed and tankiness, also jungle bonuses.
Items :
Starting with the wriggle's lantern , stay in your jungle and farm . Farm till you get the recall 2 items and if you reach level six , gank using your ult and ghost summoner spell
Your core build is hydra , bloodthirster , 2 phantom dancers and infinity edge , selling boots in order to buy guardian angel . This build will provide you with needed attack damage , attack speed ,movement speed to compensate boots loose , critical chance and durability .
Consider selling a phantom dancer to buy a warmong armor so you can push towers by yourself using your ult .

You want to rush wriggle's lantern and farm the jungle using all of your spells . The unique passive , armor , gold bonus and lifesteal will get you a very good time in the jungle .Ward the blue/red using the wriggle lantern active and the other one with the ward trinket .
You want to get money from the jungle , considering a normal monster camp will give you around 110-135 gold . Master yi's fast jungle clearing abilities are very useful for this , thus you will be getting recall 2 items in no time .Mid game you want to get the red and blue buff for more ganking power and consider soloing the dragon . Late game you want to keep these buffs and considering you reached the full build stage , sell wriggle's lantern for infinity edge and go and solo baron .

In teamfights , focus on the adcarry . Wait for your team to go in first and then go with your ult . Take all the kills you can , cause you can carry your team
In early you want to stay in your jungle and farm till you get some good items and your ult .
Gank with your ult and ghost to get money to finish the items .
In mid game you want to push with your team and be as close to them as you can , in case of teamfights . Consider doing solo dragon and counter jungling to leave your adc and midder the red and blu buffs .
In late game , do solo baron as fast as you can and ward the place . Getting a warmong can help you backdoor towers / splitpushing without minions .Use your ult for this

Dont focus jax while he is in e , dont focus tryndamere in ultimate , fiora with ultimate up , or any feed champion with a stun ( withouth a tank / off tank ) .
Use your W when you find yourself focused or in a bad situation . combine your ult with ghost homeguard and phantom dancers to fast secure your base . Q on minions in front of enemies to harass .
Master yi has a very good mid game and good late game with a poor early game.