Pros:
1) Strong Jungler
2) Strong Damage Early Game
3) Escapes Easily
4) Strong Ganking Capabilities
5) Can Counter Jungle Easily
Cons:
1) Very Squishy Early Game
2) Team Dependent (Weak lane Champions makes for hard ganks.)
3) Weak Versus Tank Champions

Lee Sin is a very versatile champion, my friends and I all enjoy playing him and we all play/build him differently and we generally all do fine. This guide is simply the way I play him. I generally do well and I feel that this is the best build for me. Lee Sin is, in my opinion, a good champion, but put in the hands of a great player will result in an amazing champion.

I use Armor Penetration Marks and Quintessences, with Armor Seals and Magic Resistance Glyphs. I find this build to be most effective for jungle play with the little magic resist needed to live through a Tibbers bomb.
I've seen others use runes such as Run Speed Quintessences, Attack Speed Marks, Dodge etc. Lets be real, Lee Sin has a very high base run speed and can use his abilities to maneuver well in team fights and general ganking. His passive also seems to be more than enough attack speed if you actually keep an eye on it. I'm not saying you MUST use the runes I suggested, I'm only saying I don't have needs for them in my play style.

I use Flash/Smite. Since I'm talking about Lee Sin as a jungling perspective, Smite should be a necessity(Especially if you take my jungling route, it is necessary). I usually enjoy having Flash as Lee Sin or any champion for that matter. However, if you feel like you will never need Flash you could grab Exhaust or Ignite.

21/0/9 is my mastery set up. Pretty basic. I would like to get the bonus armor/magic resist from the protection tree, but I find the extra length on blue/red buff + experience gain is just better overall.

Now this is where it gets tricky for Lee Sin. I stated earlier my friends and I enjoy playing Lee Sin and we all have different builds. My build that works best for ME is the one listed. I generally always go the same route. Armor + 5 health potions > Madred's Razors + 1 Health potion(Wriggle's Lantern if you get a few good ganks). > Wriggle's Lantern + Boots of Speed > Giant's Belt + Ruby Crystal > Warmog's Armor > Atma's Impaler > Mercury's Treads > Sheen + Phage > Trinity Force > Force of Nature > Madred's Bloodrazor(Sell Wriggle's Lantern).

With this complete build you will be nearly unstoppable. This build makes you incredibly tanky (I always get Warmog's Armor first since Lee Sin's abilities should suffice in damage until you are able to build a Atma's Impaler) with all the damage you get from Atma's Impaler and Trinity Force. This also gives a lot of run speed which is very good for any bruiser.

R>Q>W=E I always Rank Q first, (Although I start jungling with E, but will discuss this later.) I have tried ranking my W before E and my E before W and it generally depends on the play style. I like the bonus slowing from your E so I usually rank it out first, although if I am struggling with survivability I will rank W before E. Either way, both are very good skills.

This is where I differ from most Lee Sin players. My jungling route is Blue(level 2 gank) > Wolves > Wraiths(level 3 gank)> Red > Golems(level 4 gank) > Back > Wolves > Wraiths > Golems.

My jungling route depends on a strong leash at blue, and maximizing your passive. I am always observing lanes to try to get ganks whenever possible. I rank my E first, then my Q(or E if I don't get a good leash, if this is required then you probably will not gank at level 2). At level 3 I rank my E, then I gank. Since Lee Sin does massive damage with his Q early game, you should try to gank as much as possible to burn Flashes or make your enemies back to miss their experience, or simply kill them. Lee Sin is a powerful counter jungler as well. After you get level 4 and back to get your Madred's Razor, his jungling becomes a piece of cake.

Lee Sin is a very good team player, his slow is good and his ultimate Dragon's Rage is Amazing. Lee Sin is not an initiator, if you find yourself initiating a lot of fights (unless you are endgame and almost unkillable), then you will find you have problems with strong AP carries early-mid game. Although if you find an opening to Kick someone to your team without getting killed in the process it could work out for you. I generally like to Kick one into the rest of the team, giving your team CC and Maximizing the damage of your Ultimate. Do not focus tanks, this build is meant to kill non-tank champions early-mid game.

Lee Sin is a very good champion for me, I've won many games with him. Every Lee Sin player has their own methods and he can be played many different ways. This is just my perspective and I do very well on him.
-Champions that I recommend to avoid(situational of course)
- Amumu
- Garen
- Annie(Tibbers)
- Malzahar
- Warwick
- Mordekaiser(Children of the Grave)
- Cassiopeia
Just a few champions I have found to be a bit tricky to gank. AP carries and their ultimates usually wreck Lee Sin since he is very squishy early game.