This is a simple guide made for people having trouble making this champion work.

Here I give you the best options based on my games on other players' opinions.

This is my first guide, hope it helps.

Conqueror: I find this still the best keystone on Master Yi today.
If you don't take it, you'll have a much harder time with tanks. It's just honestly one step ahead than all the other precision keystones.

Triumph: Since you are Master Yi, expect to be doubling up, maybe tripling up on kills.
It is absolutely necessary to take this rune. Gives you extra gold for kills and heals you after you or your teammate slays an enemy. Just a good rune to keep you healthy in team fights.

Legend: Alacrity: Unless you're split pushing and need the life steal or you're against like a Gnar and you need the tenacity rune, there's no reason not to take alacrity. Just the best rune that gives you a lot of attack speed over the course of a game.

Coup de Grace: You should be ganking a lot after your level 6 power spike. Usually when you gank you'll be ganking low health enemy champions so this rune is very helpful in securing kills.