Some Lee Sin Mechanics

Kick-Flash: Instead of flashing behind the enemy THEN kicking, you can ult first then flash in a direction and the enemy will be kicked opposite of the direction you flashed to.

Ward Jumping: An essential to playing lee sin. Try putting your trinket on quick cast and change your number 6 slot to C or V. This allows faster ward placement, resulting in a faster jump. When ward jumping be sure to estimate the max distance of the ward so that you don't end up just clicking and moving. Ward jumping should be very fast in order to gain the max displacement from where you were before

Insec: We've all heard of this one. But if you havn't, that's what this is for. Insec is where you q an enemy, cast the second q, place a ward behind the enemy (preferably closer rather than max range), jump to the ward, and ult the enemy. The quickest way to do this is to ward jump before hitting the enemy with the second q. But you can hit the enemy with second q if you want to.

Laning:
When laning, constantly be trying to double w yourself and and take advantage of the life steal and spell vamp.

You dont always have to land your q to engage, if you're confident, w to a minion instead to surprise them, and e. As they are running away, land a q to do even more damage.

Jumgling:
Land your q on the monster, smite, then immediately q to do more damage.

Constantly self w, when jungling, to get the lifesteal and spell vamp.

Dragon and baron stealing is very easy with lee sin. get vision with your q, activate the q, smite, then flash or ward jump out.

When ganking, try to run into the gank. Dont q into it. Or you can lane gank and w to an ally to gank. Try to save q for last, so that maximum damage can be dealt.

[*] Ravenous Hydra: I usually build this first on lee so that he can utilize the early game damage. The active and passive synergize with lee's E, making clearing waves extremely easy.

[*] Maw Of Malmortius: When against AP mid lane champs, build this first for its MR and damage. The passive is also very nice.

[*] Blood Thirster: I used to build this on Lee because of its ability to give a ton of AD (making lee a damage god). But now it only gives a shield, which is ok. This can be built with Ravenous to give insane amounts of lifesteal. Combining all of that with his Iron Will makes him hard to kill.

[*] The Brutalizer: Very good early AD item, nearly all AD champs should build this first. Armor pen makes this a very good choice for early game.

[*] Randuins: Randuins is great for its armor and slow. Its passive (which slows AA when attacked) prevent the ADC to do max potential damage.

[*] Last Whisper: LW must be build on Lee. 35% armor pen is amazing, especially in late game where his damage falls off hard.