With Yi, it is extremely easy to farm. You should be able get first 2 item in 10 just minutes. (You should have about 100 cs) After that it is just wait 20 for enemy to surrender. Just don't forget to place wards and sweep enemy ward to save yourself from ganks. While doing 1v1 don't rush spells. Wait for your enemy to turn away and run. And when they do, use both ignite and exhaust to slow them down. This way you can easily kill them even if they make it to their turret.

This is a work in progress, please try it before downvoting. Thank you.