Well hello there, welcome to my Master Yi guide.
I currently play Yi ALOT and i've looked through the current guides and tried them out, and I discovered the way I run him works alot better for me.
I will keep this rather short and simple but try to be informative so dont expect a 10000 word essay :)

What I tend to do is harass a bit with q early game, but if i'm about to jump on them, I hit my q onto them, then my e as soon as that lands, and then your r, if you have ignite chuck that on them too, you should smash them.
Basically, to slaughter all living enemys,
Q E R (ignite if applicable)

I choose flash because its great to get away if you don't have your R or early game, you can also get over walls to help teammates.
I choose ignite because I would rather jump in with an extra (however much damage) on my side to kill someone then jump in with them doing no damage (exhaust) also ignite is great because it stops those moments when they just just just get away with a smidgeon of health, they burn! joy for all :)

You really need to be careful of CC, stuns especcially and supress's, if possible, let someone else take them, because otherwise you will get taken down rather easily.
In team fights you should try and focus the weakest (obviously) but if they are running, it is sometimes alot better to let them go, and get the rest of the enemies behind you, and help out your team.
Try not to be bloodthirsty don't put yourself in alot of risk, remember Yi is rather squishy, so dont really take people head on until you have a good item set or someones with you.
Remember if you're about to attack someone, chuck your E on! you can do ALOT of damage early on, even level 1, especcially if your passive goes off, then there goes their health.
I hope you guys like this build and I hope it works out, please dont just ignore it for being so underdetailed, I hope theres enough here for everything to work out!
Leave any comments on what I should add more too if you wish, I would appreciate it :)
Happy Headhunting Masters! :)

Sorry i've had troubles uploading the photo but I had all these games in a row (as Yi of course)
21-3-3 victory
32-3-5 victory
9-4-5 disconnect
29-8-13 defeat :/
10-2-6 victory
11-7-8 victory
all with this build as Master Yi :)
My current best score as him is 33-3-8, be sure to comment and show off your acheivements so I can see how well it works!