Hi everyone, my name is Alex and I'm a regular League player.
When I started the game I really loved Lee Sin, he is my favourite champion right now, so I wanted to make a guide in which I could tell you the things I learned in the time I played him.
Who is Lee Sin?
>Lee Sin is a melee fighter. He rushes around the battlefield dealing consistent damage with his attacks and his abilities, alternatively, he can dash in&out of combat dealing damage and short bursts before retreating. He uses energy to fuel his abilities, meaning he is more limited by cooldowns and energy regen to spam his abilities.

Lee Sin is a very difficult champion, meaning he has a lot of choices in the item section, you can go super-tanky still dealing damage, a mix between tanky and AD, which is by far the best one, and AD, which is pretty good, but letting your team behind late game.

If you go top max like this : E>Q>W or E>W>Q, this will give you super split pushing ability and high CC with your E ability.
If you go jungle max like this : Q>W>E or Q>E>w, obviously when you gank you need to hit Q, and to max the kill potential you need to max it.
Of course grab a point in the ultimate each occasion is given to you.

Flash and Ignite is the best combo for a bruiser, you can switch Ignite for TP if you think you will be dominated in lane/you will make ''surprise'' ganks/you will regroup with the team after split pushing.

Lee Sin is a very popular champion in ranked games, he can be put in 3 roles : Top, Mid and Jungle, this is what makes him so popular/banned.
When to pick him?
>When you have really good early game team/no real escape enemies(some)/when you want ( there is no real reason why not to pick him in every game )

Pros

+ One of the best in early game. + Extreme good at ganking. + Good CC. + When mastered, very hard to kill.

Every champion has his Pros, Lee is really good early with high damage/tankiness, he is really good at ganks and he has good CC..

Cons

+ Very hard to master + Weak late game + Very vulnerable to hard CC + Skillshot dependant

Lee is really weak late in the teamfights, is very vulnerable to hard CC (stuns,snares,roots,etc) and he is very hard to master.

When you are jungling use your Q trough walls to get faster there, don't forget to get sightstone. Wards are a must for Lee for crazy escapes/plays.

You can really help your team doing the ''insec kick'' : you Q in , put a ward behind the target/in front, W on it, then R into the team, which will mostly result a very fast and much needed kill for your team.

So, yeah, this is my guide on Lee Sin, hope you find it useful and it bringed you wins on ranked/normal games.
You can find me on the summoner name Deknar ( EU-NE).