Master Yi is an easy to master and is great if used well.
The 2 builds are basically the same, just different starting gear.

Pros:
[*] Tons of Damage
[*] Fast Movespeed
[*] Pro Pusher
[*] Owns Squishies
[*] Built to Hunt and Kill

Cons:
[*] Squishy early and mid game
[*] Not invincible as most/New players think
[*] Item dependent

Armour seals- for jungling
Attack Speed- for pushing and quick early-mid game threat. (still squishy)

Alpha Strike First to farm/harass and kill.
Wuju Style is second because it does.
Meditate- I haven't had the need for it in many games. Some guides tell you to get it if you're harassed by ranged champs. Well if you're being harassed by ranged champs, keep your distance, you'll get them later XD.

Jungle: Smite and Exhaust are essential i would not replace it with anything else.
Lane: Flash and Exhaust, you can replace flash if you want with teleport maybe? but just stick with my choice it works.
Just Flash to get closer, Ult , Frozen mallet slows, Hit x 9000, 32gold

there is doubt Master Yi can pull off amazing damage. BUT!!!! he is very squishy without hp items, roughly 2000hp. With Frozen mallet you'll have a lot more hp, and you can slow them! which will help a lot. as for the other gear, they give you A LOT of DAMAGE and ATTACK SPEED, which is what master Yi is all about.

Laning: Just last hit if you can, if you're up against ranged champs, stay out of their zone but try NOT to get out zoned (i.e. the area of which you recieve exp)

Jungling: start off at blue golem, ALWAYS get some to hit blue before you do. and alpha strike whenever you can to get that bonus hit proc. REMEMBER to use a hp pot right after you get hit. then move onto wolves and then wraiths, at wraiths aim the blue one first.
Head back and get that Madred's razor and finish off RED.

By level 6 you can start to gank, just either ult and run in and aim their squishes. If someone is running away use alpha strike so that you can land on him when you finish. then simple finish him off.

This is the part you can not screw up. Master Yi is very item independent when it comes to by build.
To Gank, find a squishy and Alpha strike him/her/it then ult and auto attack. If they flash away, flash or try to get in range with alpha strike. Then finish them off.
In an 4v4 or 5v5, don't dive in stay back and try to aim for a squishy or a support or carry.

To escape, either flash or ult away, if you know you're gonna die and your team is near by, turn back and do as much damage as you can to help your team.

If it seems your team is doing well without you, go to a free lane while the other team is distracted and push a lane to earn gp and exp.

try to backdoor as often as you can. Just ULT and Wuju Style and down goes a tower.

DONT GET GREEDY- Just push one tower then return to your team.
- Don't run off to chase one more kill if you're not gonna make it. Only do it if you're sure another team mate can avenge you.

Comment and rate please, I would like to know if you guys want me to add more or change something. this guide was short but i think it's enough to get the general idea of how I play Master Yi.