I prefer start jungle on Golems, then i go to writhes, wolfs and end first jungle at blue then gank top or bot according you are purple or blue team.

Remember, you should have all blue buffs and red buffs(CORE).
Red buff slow enemy at early game and little burn. Blue buff is not important than Red buff but if u want to carrying game you gotta have it, because Yi have lethan to mana "Alpha strike" skill, He uses Alpha, Wujustyle and Highlander and will lose most of him's mana.

GANKING: You have two options.
First: Start gank by alpha strike from bushes.
or
Second: Run out of the bushes on the opponent, harash opponent with red buff or without it and when enemy try to escape by Flash then use alpha stryke to chase him.

P.S.
Sorry about my English, I'm still learning.