Lee Sin is a highly aggresive jungler from early to mid game, He can clear jungle camps quickly and make good ganks with his 2 gap closers along with his movement speed slow. He's good in 1 v 1 situations and skirmishes and is a good pick for any team comp.

Lee Sin can build a mix of tank and damage. There are some builds for pure tank and some just pure damage. Tank and damage is best and reason being is going full tank will mean you will fall off and not be too much of a threat to the enemy team. Going full damage glass cannon is just stupid. As Lee you are the initiator and should be starting fights for your team.

About Me: I'm a Lee Sin main on 2000 ELO (Platinum 3) on OCE.

Standard runes.
AD marks
Armour seals
MR glyphs
I run lifesteal quints for a Doran's blade start. It gives me enough sustain in the jungle.

Standard 21-9-0
Taking 4 points in sorcery for 5% CDR
Double-Edged Sword - 2% Bonus DMG dealt and 1% bonus DMG recieved. werf
Martial Mastery - 4AD for 1 point? Holy OP
ceebs explaining errything else

Defense Tree
Standard health regen and monster damage reduction
Juggernaut cause it sounds badass.

Flurry - After Lee Sin uses an ability, his next 2 basic attacks gain 50% Attack Speed and return 10 energy each.

Explanation:
Using your passive properly is very important in the jungle. You want to autoattack twice before each spell cast on your first two. Once you have 3 skills you still want to space out but you can autoattack once between one of your spells and still get enough energy to keep casting more. It's a bit hard to explain so just play around with it. In teamfights it is very important to do this whenever you get the chance because you don't have the luxury of being able to autoattack everything since you'll be running around peeling and repositioning.
Q: Sonic Wave / Resonating Strike
Sonic Wave: Lee Sin projects a discordant wave of sound to locate his enemies, dealing 50/80/110/140/170 (+90% of bonus Attack Damage) physical damage to the first enemy it encounters. If Sonic Wave hits, Lee Sin can cast Resonating Strike for the next 3 seconds.

Resonating Strike: Lee Sin dashes to the enemy hit by Sonic Wave, dealing 50/80/110/140/170 (+90% of bonus Attack Damage) physical damage plus 8% of their missing health.

Cost 50/30 energy

Cooldown 11/10/9/8/7 seconds

Explanation:
You level this skill at level 1 so you can do a big camp really efficiently by Q smite Q'ing it for maximum damage. You max this skill first for some extra damage and because the cooldown goes down which gives you more potential to make the big plays. It helps you stick onto people even after they flash. A great tip is when you're ganking you want to them before you think they will Flash and wait to use the second part of and most of the time they will flash even with still on them. After they flash you close the gap and they're dead. Another thing to note is that (the second part of this spell) does extra damage based on how much HP the target is missing. This means that if you get the chance, you want to use it last. When you're doing objectives get in the habit of Q smite Q to maximize your burst damage on buffs.
W: Safeguard / Iron Will
Safeguard: Lee Sin rushes towards a target ally, shielding them both from 40 / 80 / 120 / 160 / 200 (+80% per Ability Power) damage. After using Safeguard, Lee Sin can cast Iron Will for the next 3 seconds.

Iron Will: Lee Sin's intense training allows him to thrive in battle. For 5 seconds, Lee Sin gains5/10/15/20/25 lifesteal, spell vamp, and armor.

Cost 50/30 energy

Cooldown 8 seconds

Range 700

Explanation:
is awesome because it is so versatile. Defensively, it allows you to save people from dying with the extra hp from the shield and by allowing you to come to their side and fight. You can also use this to escape from ganks by W'ing to an ally, a creep, or even a ward. Offensively you can use this to close the gap on people allowing you to slow them with which guarantees a free land. You can safeguard to a creep when ganking a lane when they're last hitting which brings you into melee range to combo with your spells and slow with your autoattacks (when you have red buff or phage).

The second cast of safeguard, Iron Will, gives you lifesteal and spellvamp. This makes you great at 1v1'ing, sustaining, and even allows gaining HP from smiting. I max this second because while it doesn't go down in cooldown per level, it increases the shield and the stats gained. And when you start leveling this it is the perfect time for you to transition from an early game aggressive playstyle to a lategame tank style, at around level 11-13.
E: Tempest / Cripple
Tempest: Lee Sin smashes the ground sending out a shockwave that deals 60 / 95 / 130 / 165 / 200 (+0.6 per bonus Attack Damage) magic damage and reveals enemy units hit. If Tempest hits an enemy, Lee Sin can cast cripple for the next 3 seconds.

Cripple: Lee Sin cripples nearby enemies revealed by Tempest, reducing their Movement and Attack Speed by 30 / 37.5 / 45 / 52.5 / 60 % for 4 seconds. Movement and Attack Speed recover gradually over the duration.

Cost 50/30 energy

Cooldown 10 seconds

Range 450

Explanation:
It's great early game AoE damage and great at shutting down the aspd/movement speed of people in teamfights. Most importantly it helps you slow down targets when you're ganking. It's also useful for getting some farm because Lee Sin's farm is awful.
R: Dragon's Rage
Lee Sin performs a powerful roundhouse kick launching his target back, dealing 200 / 400 / 600 (+1.5 per bonus Attack Damage) physical damage to the target and any enemies they collide with. Enemies the target collides with are knocked into the air for a short duration.

Cost 0 energy

Cooldown 90 / 75 / 60 seconds

Explanation:

One of my favorite skills in the game. , while being a fairly strong nuke, is great because of the displacement it allows. You can combo this with and to get behind your target and kick them into your team. You can also use a ward and safeguard to get behind your target and kick them. I could go on and on about different ways you can use this skill but what's important to know is that this is a very strong displacement skill. An important thing to remember is that this skill knocks up and damages enemies that are hit by the target that you kicked. This is rare but you can sometimes be able to hit 3 or 4 enemies with this ability.

Smite - Well You're Jungling. Why WOULDN'T you get this. Needed for securing baron blue etc
Flash - Used for both Aggressive and Defensive plays. Extremely useful at late game and in teamfights. Works well for Flash+

Pros
[*] Strong Ganker
[*] strong early - mid game
[*] One of the best duelists in the game
[*] Unbeatable when mastered
[*] Fun to play

Cons
[*] Can fall off late game
[*] Hard to master
[*] Q is unreliable

Doran's Blade
I prefer to start with this along with lifesteal quints. HP+DMG+Lifesteal. Best starting Item for Lee. Personal preference Build 2 DB

Hunter's Machete
You can start this for a more safer option. Builds into spirit.

Sightstone
After the Nerfs to Lee Sin's safeguard at patch 4.5 I find that sightstone is a waste of gold for Lee. 14 second cooldown Just Isn't worth it.

Boots
Mercury treads should be picked up generally for the tenacity. Mobi boots if you want to be faster and get ganks done quickly. Ninja Tabi if they have heavy AD.

Armour Items
Randuins should always be built after Elder Lizard and Mercury treads. Sunfires before Randuins if you want a bit more damage. Generally you should get both.
Don't forget Ninja Tabi and Thornmail

Magic Resist Items
Hexdrinker Is core for MR on Lee. The DMG and the shield is nice.
Banshee's Veil should always be picked up for the spell shield and extra HP regen when damaged.
Spirit visage for the 10% CDR and Unique passive.
Aegis of the Leigon is more team oriented obviously. Just don't forget to use the active!

Damage Items
Black cleaver is core for the DMG, CDR and HP and armour shred. This Is good as your team can take advantage of the shred on enemies
Last whisper is more of a carry item I just feel that BC is a better item with the stats
Hydra is never a bad choice and you can swap this for Elder Lizard later into the game If you want more damage.
Tri Force is good but just too expensive for a jungler. Only get this as your 5th or 6th Item.

Always put pressure and make presence. Lee Sin is a monster early game with strong ganks and fast clears in the jungle. Never forget to counter jungle. 99% of the time you will beat the enemy Jungler if you don't miss your.

Your normal setup for ganks would be to something then use to follow up. You are also very squishy at this time in the game. So if you are ganking a tanky top (ie Renekton) and get counter ganked by their pantheon. This would normally mean death for you if you dont flash.

Now is the time to group, steal buffs and get that dragon.
By now you should be a little tanky and have maybe 2 of your core items.
Do not be afraid to engage fights. This is what your supposed to do. Kicking an enemy carry towards your team is probably the best thing you can do unless it is a really fed eve or something then you shouldnt kick that person towards your team. You are still very strong in mid game and should abuse your power. Never be afraid to counter jungle. Lee Sin can duel pretty much anyone in the game. Lee is also good at soloing the dragon once you have elder lizard. save your trinket for ward hopping over the wall if you get caught doing dragon. Get a pink and clear enemy vision of river or tell your support to use sweeping lens to clear for you.

Now this is where the game actually gets hard for you. By now you have to either go in ham for their carry or be a peeler for your carries. Vision control - At this point of the game. If your team is constantly fighting or fighting over baron, It could be worth getting a sightstone and upgrading to the vision totem trinket. NEVER FACECHECK I shouldn't even have to say this. Lee Sin has his Q for checking brushes. You can also use sightstone for ward hop and 'insec' kick a carry towards your team.

Don't be afraid to go in deep to kick them towards your team. It's the best thing you can do at this time of the game. Just don't go in ham. You will most likely have fallen off at this point.Once you have used all of your cooldowns and have nothing left your just a sitting duck and can get kited very easily. Make use of your abilities or you might just die by that fed Vayne if you don't.