You take smite for killing drake/baron/blue- and red buff/golems and so on. You take smite so you can be safe in your jungle. An example: You're invading an Amumu. He crys so hard, that his team appears while your team is farming. They come from each side, and you're 90% sure that you w on't get out without flash. You flash over a wall, and you're save. You can use your flash to flash behind people as well, and kick them into your team, which is a great move to do, to start of a teamfight.

You should invade your opponent jungler as much as possible, that's why you go flat ad + mr + armor. When you see oppotunity to gank a lane, go do it! Always care about enemy wards -> They might spot you out, and go call their own jungler for countergank, which sometimes solves in a bad situation for you. If your team calls for you, go help them! you're a jungler, and you have to make some good early game pressure, so they can farm and get some kills.

You go offensive masteries, so you can invade your opponent and make some strong early ganks, which solves in kills, that your team will appreciate. If your team calls for ganks, go help them -> It might lead out in kills -> If you do not response to their call, they might die, and start blame you for their death. If you play Lee sin against an amumu, you can go grab your red and blue buff, and go invade his red buff, he might not be done with it. If you can catch him out, you can be able to kill him 1 vs 1 with no problems. If you kill him before he finishes with his red buff, you can go grab his redbuff, his wraiths and his golems. Remember! if you play against junglers with AOE damage, never clear wraith/wolf camps, they hate to clear 1 little wraith/wolf + they get nearly 0 experience, while you got experience for the big wraith/wolf

You max your Q to deal as much damage as possible to the enemy as fast as possible. After that, you max W so you have sustain and you can be like a support( with the shield ) to protect your ap/ad carry mostly. Level up R always when you can! You start with E to damage as much as possible to wraiths/wolf camp. At level 2 you take Q, so you kill the other blue or red buff as fast as you can, and then you take W for jump. Now you're ready to gank or invade. If you invade, you have to play against a bad early game champ like for example Amumu. He has no escapes, no great damage abillities, while lee has so strong early game with Q/E/W. If you're against an agressive jungler like xin zhao, you might just go gank a lane, and give your lane an advanged which is good as well

START WITH

YOU START WITH THESE ITEMS, SINCE HUNTER'S MACHETE IS KINDA THE BEST JUNGLE ITEM, AND FIVE POTS MAKES YOU MORE SUSTAINABLE. AFTER THESE ITEMS, YOU SHOULD GET MADRED'S RAZORS AND BOOTS.

CORE

WHEN YOU PLAY TEAMRANKED, OR JUST WANT TO GO A BIT MORE SUPPORTISH AS LEE SIN, AND HELP YOUR TEAM GET STRONGER!

WHEN YOU PLAY SOLOQ, OR PREMADRANKED AND YOU WANT TO PLAY LIKE A CARRY. I WOULD RECOMMEND THIS BUILD MORE FOR SOLOQ THAN PREMADERANKED, SINCE THIS BUILD IS KINDA A BUILD, WHERE YOU WANT TO MAKE FIGHTS 1V1 OR 2V2, BUT IF YOU'RE REALLY FAR AHEAD IN PREMADE RANKED, IT'S NEVER BAD TO HAVE THESE ITEMS

YOU BASICALLY TAKES THESE ITEMS, IF YOU'RE EITHER AGAINST A STRONG AD TEAM OR AP TEAM. IF THE ENEMY AD CARRY IS RLY FED, YOU SHOULD GET "RANDUIN'S OMEN" OR IF YOU'RE AGAINST A BASICALLY AD TEAM. YOU BUY "MAW OF MALMORTIUS" IF YOU'RE AGAINST A MIDLANE AP CHAMP, WHO HAS A HIGH BURST DAMAGE LIKE LUX. MAW OF MALMORTIUS MAKES YOU MORE SAFE, SINCE IT ABSORBS A LOT OF AP DAMAGE. YOU CAN ALSO BUY IT, IF YOU'RE AGAINST MORE AP THAN AD. SUNFIRE CAPE IS JUST AN OVERALL STRONG ITEM ON LEE SIN, BUT YOU SHOULDN'T BUY IT, IF YOU'RE AGAINST A STRONG AP TEAM.