yi is all about attack speed for me. When i play him i take the ability ghost and clarify.
ghost helps in chasing people down and clarify is for the mana. my yi build should end up giving you 100% critical strike or at least close to it but the boots are the main part

i try to max wuju style 1st because it deals extra damage to enemies and along with ghost and boots they will receive much more damage. but be cautious when you use your abilities. since yi isn't exactly a turrent diver obviously avoid turrents when chasing people down. then second i work on alpha strike to max. but before that get a little bit on meditate, because recalling takes a long time.alpha strike is helpful when you are in the brush and you want to kill the enemy but you need a quick attack. Unfortunately it is also a great kill steal ability.
and if you play yi write he should end up not being a tank per-say, but being a really helpful supporter and kill steel er.

Many times yi as the potential to kill steel from alot of ppl. but remember if yi doesn't get helped in a gank you are in trouble. unless you have a turrent. and because yi along with boots highlander and ghost can run super speed he can help the team chase down kills.

farming at the beginning may hinder the overall outcome of the game. yi's abilities help a lot in-order to farm quickly and get money, since the stuff i buy actually aren't so cheap. wuju style or the third ability is a great farming technique at the beggining but later it should be preserved for turrent and chasing enemies down. Yi's first ability is probably the secvond most important attack as of farming minions. if yi targets a minions he doesn't just damage that minions but numerous other minions. What this means is: you can be sitting in the grass or shrubs letting the minions fight and then just kill them all at the end for the money and exp

i haven't unlocked flash yet . but i presume that flash is a great getaway technique as yi 's downfall is stuns. Since i am a lower level i like to stick with: ghost for getaways and clarify for mana for meditate. Im not exactly sure if clairvoyance or anything would be help ful for anything other then figuring out which directions enemies are running if they are running