Greetings Summoner!
Master Yi is one of the champions that I main. This is my first guide on Master Yi . I chose to make this guide for I have nothing else to do without internet (currently using cellular data). Feedback is crucial to improving my guide!

Master Yi is the Wuju Bladesman of Ionia. His role is to usually play as an assassin. He is considered an "easy-to-play champion" by a lot of people, but he is quite difficult to master. For example, his Alpha Strike ability and Meditate ability are hard to time. Timing is a key aspect of distinguishing a "bad" Yi from a "good" Yi.

Pros
+Strong Mid-Late Game
+Can single-handedly carry a team
+Massive AD
+Quick jungle clear
Cons
-Poor performance early game
-Vunerable to jungle invasions
-Squishy champion
-Hard to time Alpha Strike and Meditate
-Focused in team fights
-Can fall behind if you have a rough start

Master Yi has 4 unique abilities and 1 infinite passive.

Double Strike
Alpha Strike
Meditate
Wuju Style
Highlander

Double Strike is a infinite passive that allows Yi to strike twice after every three consecutive AAs, dealing 50% AD that applies on-hit effects and can critically strike.

Alpha Strike scales with 100% AD, can hit up to 4 enemies, and can critically strike. Yi is untargetable during the duration of the ability and he appears next to the enemy that it has been casted on. Basic AAs reduce the CD of Alpha Strike by 1 second. This ability deals extra damage to jungle monsters and minions.

Meditate allows Yi to channel for 4 seconds, gaining HP for the duration of the ability. Yi heals 1% more for every 1% of health he is missing. While Yi is in his Meditate ability, he takes reduced damage from champions, jungle monsters, and towers. Damage reduction is halved against turrets.

Wuju Style's passive grants Yi 10% bonus AD. It's active grants Yi true damage for his AAs and scales with 25% bonus AD.

Highlander's passive reduces the curret cooldown of Yi's abilities by 70% when he gets assists or kills. Highlander's active allows Yi to multiply his movement speed and attack speed. He is immune to any slows while his ability is up. Assists and kills extend the duration of his ultimate for 7 seconds.

I like to start Alpha Strike > Wuju Style > Alpha Strike > Meditate
If you don't have enough hp for a full clear, get Meditate third for sustain. Try to use it when you are low as you gain 1% more hp for every 1% of your missing health.

Most people get their Meditate third.

Run Smite and Flash for Yi Jungle.

Alternatives for Flash:
Ghost
Teleport

Other spells will not help Yi as much in my opinion. You can choose to use other summoner spells if you want to though.

Greater Quintessence of Attack Speed improves jungle clear and more DPS
Greater Mark of Attack Speed improves jungle clear and more DPS
Greater Glyph of Scaling Magic Resist reduces damage intake from AP spells
Greater Glyph of Scaling Cooldown Reduction improves jungle clear and allows Yi to use his abilities more often
Greater Seal of Scaling Health grants Yi extra HP early and late game

Alternatives:
Swap out Greater Seal of Scaling Health for Greater Seal of Scaling Armor or Greater Seal of Armor

Fury : 4% increased attack speed; faster jungle clear
Double Edged Sword : Deal 3% increased damage, recieve an additional 1.5% damage; more damage
Vampirism : 2% increased Life Steal & Spell Vamp; heal from AAs/Alpha Strike
Battering Blows : 7% increased armor penetration; deal more damage to tanks & shred through base armor
Fervor of Battle : More damage from stacks that come from AAs (deal more AD the more stacks you have); more damage whilst fighting

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Savagery: AAs deal 5 bonus damage to jungle camps & minions; faster jungle clear
Assassin : Deal 2% increased damage to enemies when your teammates aren't around; better 1v1 potential
Merciless : Deal 5% increased damage to enemies below 40% HP; more damage
Dangerous Game : Kills & assists restores 5% of your missing HP and MP; pairs along well with your Highlander

Creeping

I like to use my Alpha Strike to clear minion waves. Remember that you teleport to the target that you used your Alpha Strike on, unless they died from the ability. I use my ability on the nearest minion to get the safest and easiest opportunity to get cs. Don't use your Wuju Style to get cs because it is best used for dueling. People may dive you if they know your Wuju Style is on cooldown.

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Jungling

Purchase a Hunter's Machete and Refillable Potion for your starting items. On the Red Side, start at the Krugs.
On the Blue Side, start at the Krugs aswell. I choose to go for the Krugs to get the red buff right after.

Tip: Use your Alpha Strike to negate damage from the camps by using it to dodge AAs from the jungle camps. Use your Alpha Strike right before you are about to get damage to dodge the AAs. Also, use your Meditate when you are low to get the maximum potential out of the ability. It heals 1% more for every 1% of missing health you have.

On the Red Side, I like to start at the Krugs. Smite early to obtain the buff and AA the Ancient Krug. Use your Alpha Strike to finish off the big Krug. Next, finish of the smaller Krug with AAs. Third, put a point in your Wuju Style and move on to the red buff.

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AA the Red Brambleback and use your Alpha Strike to dodge hard hits from the Red Brambleback and Cinderlings. Activate your Wuju Style when you have your Double Strike to make maximum use of the 5 seconds of Wuju Style. Smite the red buff when you are low. BE WARY OF THE ENEMY JUNGLER INVADING YOUR JUNGLE. You can choose to ward the bush behind the red buff. Put anoter point in your Alpha Strike and move on to the Raptors

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AA the Crimson Raptor once and use your Alpha Strike right after to dodge the damage from the raptors. Use your Wuju Style to finish off the big Raptor if you have it.

It is best to gank a lane when you know that your opponent(s) don't have their summoner spell(s) (usually flash).

Use your Highlander in the river bush, use your Alpha Strike to dive in, and activate your Wuju Style for AA damage. You may choose to smite your opponent before you start AAing to deal a lot of damage and take reduced damage.

Be wary that the river bush is usually warded. A Vision Ward or raptor buff will help you check if that bush is warded. Try not to gank early game unless it is urgent that a gank is needed.