We know Master Yi Well...The Oped cheap slaughtermaster with hi attackspeed and easy gameplay.I've checked some of the most ranked Master Yi Guides and i was disappointed when i saw how stupid ideas ppl had...So here is MY Master Yi Guide for hose who want to Level up Faster and win 3 v 3 games in 14:35(my record)
This build Mostly about attack speed mowement and the passive bonus of Wuju style.This deadly combination really can bring foes down

For runes....i think you only need attackspeed mostly...But you may put in some armor pen.marks and/or quintesences or Eeven critical chance...but it's a whatever thing
I prefer attackspeed runes because at the begining they are muchmore useful than a crit chance or an armor penetration rune and in the later game they give you high advantag against most of the enemy champions

The Masteries are clear i guess.You max out Awarness for getting advantage in XP against those who hadn't didi it and it's very good if you are alone,leveling in a lane
The offensive masteries are quite simple...i mean there are no useful skills only those i've chosen...

Pros:

Very fast mowement
Awesome attack speead and damage output
Flee and Chase is easier than ever!
Easy travel over map/assasinating

Cons:

They will focus on you pretty soon
One word:Thornmail
you shud watch out for ganks!
Swishy and low armor
Tanks are hard to take down beforeLast Whisper

The "heart" of this build is the item selection first you should pick an atack speed dagger or a Boots of Speed and 3 health Potions this are the items you should start with.at the second hand,aftr first blood(that definetly will be yours),you should get Boots of Swiftness as soon as possible so you may chase ranged and melee(so easily) and you can also flee(sometimes important).After Boots start to create two Phantom Dancers.This three items are the core of the build.You can smoodly win a game with only these ones but just for fun after you have these create an Infinity Edge so the atack speed and critical chance/powe combination will anihilate most of the champions in game than you may create a last whisper or a Black Cleaver...whichever you want...they are good against tanks and such things...

Skill sequence is very easy for this build...at LvL 1 start with alpha strike.It's good for chasing,lasthitting and such things.At LvL 2 put your point on Wuju Style because this will be your Core Ability max it as soon as possible or you may incrase it with Alpha Strike Level By Level.If you can put pints on your Ultimate also but Meditate is just not important because you have atacksped from Runes and items and Atackdamage from Wuju strike so noone can stand in your way.

I've chosen Exhaust and Ghost....Ignite can be helpful also but you are faster than the enemy so he cant flee or if you are not faster you have Exhaust and Ghost(even good for fleeing)
Also Exhaust is very Handful at the first Blood Before you go up Laning

Other Summoner spells:

Claievoyance:...just simply useless as in most cases.

Ignite:It's also a good choice..some bonus damag.Especially good if the enemy has healing support or great lifesteal.you can put some extra dmg on.

Cleanse:I dont think it's needed...your ultimatesolwes any problem like this

Fortify:simply just not useful for you...not so ofensive at all.

Heal:Sometimes it's good but i think you can put out enough damage so u wont need any heal or such.

Clarity:You may find it useful at the very begining of the game cuz sometimes u can run out of mana very quickly and it's hell annoying but i think it's not so important.Get a support near you and i think he will have some Clarity for you.

Flash:You can move faster than you may travel with flas...after the second Phantom Dancer you really wouldn't need thi so donteven pick it.

Smite:If you Jungle...it's useful.Anyway i dont really think you want to.I never pick it with Yi...

There are two very impotrant things about you and your team.

First:Make sure that you will go up after FB!Ask your teammates pleasantly.There is only one case when you shuld stay down,if a vey strong ranged(Teemo) is against you up

Second:Always watch out for Teamfights,the minimap and your teammates because with your movement speed you can easily travel in the map ad with your presence,teamfight are won

This was my Master Yi Guide.I hope you Like it and that you'll try it.
It wasn't a very Big work...very simple.But also very efective!
I wait your questions below!

Wishing you many kills(except if i'm the opponent)!