Master Yi is an easy to learn high damage champion and not really that hard to master him. All you have to do is time your Q right then kill the squishiest first then you get your penta, That is Master Yi.

Pros
-Very High Damage
-Can Splitpush Like God
-Easiest Penta In The Game
-Easy To Play
-Easy 1v5 When Fed

Cons
-Very Squishy
-Vulnerable To CC(But can be dodged using Q)
-High Manacost Early Game
-Weak Teamfighting Ability
-Bad At Ganking(No CC)

For runes, you equip Attack Speed runes. 41.4% Attack Speed is too good for Master Yi especially on early game since you clear camps faster. Full attack speed runes is good for this build since the full build makes you kill squishies in 2-3 autos and the build doesn't give you much attack speed so these runes pretty much answers that problem for you.

His Q is one of the most annoying skill for other players ever. Can dodge ults and skillshots like a boss. Can disjoint other champion skills and more. Real OP when used right.

If you are behind, just keep CSing and clearing the jungle also you can KS! That way you can outfarm them and rekt them late game. Your goal is to get your core item and they can pretty much do nothing about you. You can squishies in few autos.

When a team fight occurs, never engage even when you see a front line squishy. Wait for your tank to engage or for your team to engage first then you ult and clean up the fight. Never engage even the enemy carry looks juicy. NEVER GET GREEDY, especially in this build. Wait for them to get busy then you clean them, that will give you Quadras and Pentas.