This is my First build so please tell me what you think, you want to start with his WuJu strike because it helps when you gank to take off a lot of damage per hit so you can kill them faster, and because it helps in the jungle quite a bit.

I use standard dps jungler runes.

Armor pen reds and quints, armor yellows and magic resist per a level blues. You can throw attack speed quints as you please, it will help you jungle faster but hurt your mid/late game more.

I use standard 21/0/9 for jungling. Nothing too special with my masteries here.

For my starter items I get cloth armor+5 potions. After completely my first route through jungle I grab boots and 1 or 2 more potions.
Grab wriggles and then your berserker's Greaves if the enemy team has a lot of cc i would recommend getting Mercury's treads, however it doesn't matter that much cause in this guide i sell the boots after the second phantom dancer but if they have to much cc keep it and don't get either a Starks fervor or a Bloodthirster.

If I am farming really well I will straight rush my Infinity edge, and if I am not farming well I will grab a zeal before completing my infinity edge.

Once the infinity edge is done I go for a phantom dance then some life steal.

I like flash/smite on Yi but I have been experimenting with teleport/smite for super split pushing. Both summoners work well so it is all preference.

As Jungle Master Yi you want to start off with the golems, smite one and finish it off, afterwords you activate your WuJu style and finish off the other one, after that you want to get Ghosts then go on to wolves, then try to gank someone or if you cant then get blue. afterwords you want to get Golems again then go for red and then you can either take their jungle (unless they have a jungler) clear your jungle or gank someone else, after that you can just kill whatever you want(but not Dragon until you have your Wriggles)and gank when you see the opportunity, have fun.
Video of Jungle Route Below Play Video Remember this is not my Video so give the Credit to StoneWall008 he made it not me.

Yi is pretty poor in team fights unless extremely farmed. Outside of cleaning up a team fight you should usually not participate in team fights heavily.

Instead you should be split pushing lanes constantly farming. Your goal is to farm EVERYTHING on the map and have more farm than anyone. Keep constant pressure on lanes at all times. When you are split pushing also use wards to keep yourself safe and see the enemy coming.

If you are pushing bottom lane then ward the brush near the lizard camp. If you are pushing top lane then ward the bush at blue golem. Reverse this if you are playing blue side.

Try not to engage people while you are split pushing unless you know where everyone else is on the map. Yi can kill almost anyone 1v1 however don't be greedy and get caught chasing down a kill. Your main goal is to keep farming and to push towers down not to grab that kill. So keep that in mind!

Once you have your core items and are farmed a god awful amount you can participate in team fights but until then you choose the fights because you have your ultimate and can't be caught. So let the enemy play your game and bait them around the map.

One of my favorite tricks with Yi is to tell my team to wait somewhat near baron. Then I push bottom lane really deep and bait the enemy team into chasing me. I laugh and taunt the enemy team as I run away while my team gets a free baron. You would be surprised how often this works.