Lee Sin is a melee fighter that has 2 abilities in 1 skill. Lee Sin can do many things in battle. Lee Sin is able to jump into battle harassing squishy targets and able to cause crowd control for the team during a team fight. Lee Sin can jump to a(n) ally minion or champion during a fight or when an ally is low on health. Continue reading and I'll tell you more about Lee Sin, I will be explaining the runes, masteries, skill sequences and summoner spells and why it's important. Enjoy the guide while you read, I hope this guide helps you. Thank you.

During champion select, the summoner spells I choose for Lee Sin would be Smite/Exhaust or Flash. Always be sure to check your team's summoner spells, if they lack exhaust, use exhaust as your spell because it will be useful during a team fight. I use Smite/Exhaust because I get used to using my W skill (Safeguard/Iron Will). Also, in team fights I would exhaust the squishy target for my team to pick up the kill and continue pushing lanes afterwards. Another spell I use for Lee Sin is Smite. I prefer Smite for Lee Sin because Lee Sin is very good at ganking lanes due to his Q skill (Sonic Wave/Resonating Strike), when you gank a lane, you are able to use your q and jump to that target that you hit and harass the enemy champion along with your allies to pick up the kill. Lee Sin is very good at jungling because of Safeguard/Iron Will, when he casts Iron Will, he gets lifesteal, able to stay in jungle longer, instead of recalling back to base.

The runes I use for Lee Sin is:
9 Greater Mark of Desolation:
2 Greater Quintessence of Resilience
1 Greater Quintessence of Desolation
9 Greater Seal of Resilience
9 Greater Glyph of Resilience
I use armor runes for Lee Sin while jungling because I noticed that I take a lot of damage at blue buff after finishing the wolves. So I picked up a few armor runes to stay longer in jungle.
I also use a few armor penetration runes to maximize my damage when I start ganking. I do not use attack speeds runes because of Lee Sin's passive, Flurry. Each skill Lee Sin uses, his passive is activated, which means he gains an amount of attack speed for a few seconds.

Jungle Route
There are two ways in jungling with Lee Sin. You can either purchase the following:
Vampiric Scepter OR Cloth Armor and 5 Health Pots
In the beginning of the game, I will buy a Vampiric Scepter when I start jungling. When I hit level 2, I would add Safeguard/Iron Will, gaining more lifesteal later on.
Wriggles Lantern/Boots of Speed/Sight Wards or (Vision Wards, if needed)
When I recall, I get a Wriggles Lantern to place down wards in rivers or important places like Dragon or Baron. After purchasing a Wriggles Lantern, I would then buy a Boots of Speed, continuing later on to get Mercury's Threads.
Giant's Belt/Ruby Crystal/Regrowth Pendant (Heart of Gold is optional)
After ganking a few lanes, you may either gotten assists, picked up a few kills, farm while watching your allies' lanes or continue jungling. You should be able to purchase a Giant's Belt/Ruby Crystal and a Regrowth Pendant, creating a Warmog's Armor later.
Atma's Impaler/Negatron Cloak
After purchasing your Warmog's Armor, you should start building an Atma's Impaler because of it's passive. You should be able to do damage during mid game around 20:00 - 30:00. After building your Atma's Impaler, start building a Force of Nature for extra movement speed and magic resistance, either the enemy AP carry is fed or there's just too many AP in their team.
Guardian's Angel
During late game, you should build a Guardian's Angel for more armor and magic resistance.
Bloodthrister
Wriggles Lantern is probably useless during late game. Sell the Wriggles Lantern and start building a Bloodthrister for lifesteal and damage stacks.