Hi everyone!This is my first guide on mobafire...I hope you will like it.And btw sorry for my bad english!
After playing some games with Lee Sin i found out that he is extremly powerful when played right and can 1v1 a lot of champions easily and can help in fights by killing key targets fast.

For masteries i do 23-6-1 taking many improved offense,basic defense and improved ghost and exhaust!
If you want to go more tanky i suggest 9-21-0 for more survivability and for jungle you can go 21-0-9 for more xp , buff duration etc.

For marks i take armor pen for more damage.
For seals i take armor for more survivability.
For glyphs i take magic resist for even more survivability!
For quints i go for armor pen but you can also take health quints if you feel you die fast.

For Lee Sin i take exhaust and ghost ,working out very well with him.
Exhaust is good for slowing enemies,making it easier to catch them and for killing them easier reducing their damage.
Ghost is good for catching up enemies and escape tricky situations.
You can also go with flash but you already have a blink with your shield and with ghost should be easy to escape.

I prefer to max out Q first because this is the most important ability on Lee Sin giving you a lot of damage.
After Q is maxed you can max the other skills in any order!

I start out with a long sword and a health pot because the +10 dmg from sword is very good early game.You can also start with a doran's blade but i prefer long sword to get earlier brutalizer.
For boots i choose berserker greaves because you need that attack speed boost but you can also go for boots of swiftness for more speed or for mercury threads if they have a lot of CC!
After i finish my boots and brutalizer i take a phage and finish my frozen mallet.Frozen mallet is very good on Lee Sin because it give you lots of hp,dmg and slows enemies.
Next i finish my Youmuu's Ghostblade.This item gives you dmg,armor pen,cooldown reduction.Everything you need!
I choose to take last whisper for high armor pen and even more damage!
I rarely get to these items but if your game isnt finished and you are done with the first 4 items i suggest taking trinity force because it gives you a little bit of everything and madred's bloodrazor for more survivability,dmg and attack speed!

Here are some tips and tricks for this champion!
First off i got to mention that after you cast a spell you should hit with 1 or 2 normal attacks to benefit from your passive!
When you try to kill and enemy you should hit him with Q then ultimate and then activate Q again to get to him after the knockback.This is how you maximize your damage without loosing your opponent.
In fights also try to hit your ultimate so that you can push your enemy in your teammates or turret.
In the laning phase you should try to harras your enemies with your Q and E ability and then back off with your w ability on a creep or ally.You can always use your W to save allies or save yourself with that blink.
In fights you should use Q and E combo as much as posible and use W to save allies or yourself.

So thats how i prefer to play Lee Sin,and incredible champion when mastered.
Im waiting for your comments and tell me what you think about this!I will check it daily and update it as much as possible after your opinions.
I will work on a jungling build after more testing!
And dont downvote unless you tried it and if you downvote leave a comment with reasons!