I am not Ranked, I am not exceptionally skilled.
However, I have played against many different Yi's as Yi and they have often asked for my/for me to post my build. They will be using other Mobafire builds, and their builds just cannot keep up. I have gotten 30+ kills in blind pick Twisted Treeline 5v5 matches, more that once. So, here goes.

Start helping top until you are level 5. At this point you should have enough for Vamp. Scept. and at least a Dagger, if not Zeal. Focus on harassing the enemy top laner, and try not to take too many minion kills. This will give both you AND your top a large advantage early-game, and allow you to get back to the Jungle to take your buffs before the enemy jungler can counter-jungle.

Gank, gank, and gank more. Its what you do best. Get your buffs when they come back up, kill monsters whenever you have a free moment. Get ganks, buffs, and monsters. You should be able to kill dragon between levels 9 and 12, depending on how much gold you get.

Wait until there is a drawn-out teamfight going on somewhere, preferably nearer you base, and push either bottom or top. You can usually get an inhibitor at the point and your team will win. With your ult, you can tank a turret (Though unadvisable). And you can 1v1 basically anyone, so don't be too afraid. You can 1v2 many combos. Just be careful if they have a stun/blind and you don't have a Mercurial Scimitar.

Levels 1-5 can be a problem if not careful.
6+ you can really start getting ganks, with your ult.
By the time you reach level 12, you should've slain slain the dragon, and begin really snowballing. At this point, it get easier.

Watch out for Thornmail: it can be used to counter your crazy attack speed/damage by causing you to damage yourself.

You have very little health. Try to get the first attack in, and your Q is a great distance closer.

Master Yi is easy to learn, but very hard to master.

Above all,
Have fun!