This guide is meant for those that don't know how to use Yi, and just build his recommended items, which in my opinion is stupid. This guide will show you how to get fairly high damage output as well as decent attack speed early game. As well as, how to become less squishy and finish with a fairly good score, depending or not whether YOU are fed or YOU fed. Let's get started shall we?

Pros:

High Damage Output
Fun
Most games Carry
BEAST when fed
Great backdoor-er

Cons:

Squishy
Most people say he's a nooby champ

For runes, I go with simple Armor Pen Quints, Armor Pen Marks, Flat Armor Seal, and Flat Magic Resist Glyphs.

I go with the regular 21/0/9 mastery setup, getting the final mastery in offence. The more damage the better.

I usually start off with Boots of Speed, but Doran's blade isn't bad either. It helps with last hitting early game since it give extra damage and keeps you in your lane a bit longer with the HP boost. But if you feel like you don't need it, go with Boots of Speed and 3 Health Pots. After getting a sufficient amount of gold and recalling to your base for the first time (given that you stayed in your lane long enough) you should be purchasing Berserker's Greaves, if you have enough to buy a Recurve Bow, then purchase it. If not, then getting a Dagger wouldn't hurt either. Proceed with making Sword of the Divine, this really helps early game giving a huge attack speed bonus as well as a good passive and active. Now what good is all this attack speed if you're barely doing any damage? That's when you purchase your first B.F Sword. If the game is going well for you, then I would purchase Black Cleaver right after. If you aren't getting enough gold, then I would suggest buying a Vampiric Scepter, after that, go straight to a Black Cleaver. The Zeal should come next, and then start saving up for that Infinity Edge. Once you have that beastly item, complete your Zeal by upgrading it to a Phantom Dancer to have that bonus in Crit and Speed. If you get to here it should be near end game. So you could purchase a Bloodthirstier to end things quickly if you're doing well, but if you are having difficulties with the enemy team then you should consider buying these items. Madreds Bloodrazor for those Tanky Champs, Banshees Veil for those pesky Mages, 2 Bloodthirstiers for those with Thornmail or a Frozen Mallet if you feel like you die to quickly. Although if you end up having a good team, and the other team isn't fed, then you should have no problem and stick to high damage output items.

I usually start with Wuju Style, it helps with last hitting and this guide is basically meant for Wuju Style, you could also start with Alpha Strike then Max out Wuju Style. So I max out Wuju Style, Alpha Strike, Level up Ultimate whenever I can, and Meditate when I'm forced to. You can just follow the skill sequence above.

I usually take Exhaust and Ignite with me, in my opinion, these 2 spells suit Master Yi the best. When you're 1 v 1 someone and they try to run, you can pop exhaust and ignite, and finish them for an easy kill OR if you're fighting them to the death pop both spells and even if you die, you might get the kill with ignite. In some instances I managed to survive with minimal HP because I popped exhaust to reduce the enemy's damage and dealt enough damage with ignite to kill them quick enough for me to survive and recall. But in the end, it's your preference. Here are some alternatives : Flash and Ghost. Seeing as how his Ult gives you bonus Move speed, I don't really see the need for these spells, but they are useful for escaping. I don't recommend taking these spells for Yi : Heal, Revive, Teleport, Rally and Clarivoyance.

This guide is meant for laning with a partner, either top or bot, don't solo mid, because 9 times out of 10 you'll be going up against a range champ, and Yi doesn't do too well with range champs. This is a Wuju Style/Crit type of Yi, not an AP Alpha Strike/Meditate Yi. FYI I know he's an easy champ to use, but I see so many Yi's that struggle, this is simply a guide to help them get better with AD Champs.