Lee Sin is very good early game so you want to clear gromp/golems ( smite them for buff ), both buffs ( you will end with about 60 - 75 % hp), and then go gank. Don't forget to ward jump :), then go back. You MUST buy Stalker's Blade, because you will be ganking a lot and if you have enough money buy boots or sighstone(+sweeper). Generaly you will continue to gank and farm only buffs and crab, but clear crab only if you don't have anything else to do !. If bot is even or your bot is winning, try to gank them when about level 6,7 and if you succes you can get dragon ! Since you have sightstone sometimes ward Dragon or Baron ( when its up and you can't take it), to make sure enemy team will not get it. After level 6, without excuses -- NEVER smite for clear. Use it only for ganks or Dragon and Baron. If all of your lanes are losing, focus only one, where the enemy seems killable and is the biggest threat for your succes of winning the game. If you are winning make sure you will get as much dragons and Baron as you can and increase the advantage. I think thats most of the thinks you will need, good luck and train Lee Sin mechanics :)