This is a guide to one of my favorite champions, Lee Sin. Lee Sin takes some practice to play well, but he is a fun and rewarding champion. The best way to learn I would recommend watching someone who knows plays Lee to get an idea of what to do with him. Anyways, Lee is a beast of a jungler. He has incredible mobility with two dash like moves, that can go through walls. He has healing, damage prevention, slows, a move that reveals stealthed champs. He is based on energy, so you don't ever have to worry about being low on mana. His energy recharges very quickly, and if you use him right, you will always have a move ready. Lee Sin is a total baddass.

For Marks, I use Armor Penetration. Armor/Magic Resist per level in seals and glyphs. Flat hp Quintessences.

I have my masteries set at 16-3-11.
Under offensive masteries, improved in smite, improved critical damage, armor penetration, and bonus attack damage.

In my defensive masteries, I have bonus armor for jungling.

In utility I have 3 points in hp regeneration, improved ghost, bonus exp, and longer monster buff duration.

Standard Warmog's Armor and Atma's Impaler combo.
I start with a vampiric scepter. Jungle.
cloth armor, long sword, working towards a Wriggle's lantern.
Then Mercury's Treads.
Warmog's Armor.
Atma's Impaler.

After that, I really like Sheen. Lee pumps out special move after special move, and Sheen will boost his normal attacks a lot.
Maybe transition that into a Trinity force.

Another nice option, Frozen Mallet. Adds slowing effect to your hits, plus the additional hp boosts Atma's impaler as well.

Banshee's Veil is a good option if you're facing a lot of AP.

So in 5v5, I go start in the wolf camp. Move on to the Wraiths, using smite on the blue wraith. Then go to the two small golems. Then Blue buff, red buff.

By level 6, Lee can solo the Dragon with a Wriggle's Lantern. It's possible.

3 of Lee Sin's special moves can be used to aid your teammates. His W ability, Safeguard is an obvious shield. Save your teammates from turret hits, Karthus's ultimate, etc. His E ability, Tempest can be used to reveal stealthed units in an area around you. The second part of his E, cripple, can slow enemies down for your team to chase down. Lastly, Lee Sin's ultimate, Dragon's Rage, kicks enemy champions away from you. You can use it to kick a champion towards your teamates, or for escape by knocking your pursuers away. His ultimate is very useful especially when ganking an overextended mid champion.

Pros
[*] Very mobile
[*] Good at chasing down enemies
[*] Area of effect move pwns stealthed enemies
[*] Area of effect move pwns enemies.
[*] Tower dives really well
[*] Ultimate kicks people into outerspace

Cons
[*] Deals mostly physical damage
[*] Blind