Depending on who you are against your jungle path varies, a smart thing to do would be to start the opposite buff to your opponent and take his buff in his jungle. Then proceed towards his golems, take the big one and leave the small one so he does not gain as much xp. Retreat back to you jungle and kill your wolves, wraiths then golems. Once you have done this and if you have health left you can begin to gank lanes. Bot or mid is a good place to start depending on which is losing. As soon as you have made some ganks and helped the lanes out you should get back to jungling to keep up with your opponents, clear some of your camps but make sure you're moving about his jungle and taking the big wraith, wolf etc to lower his xp and take him off his game.

If you find yourself wanting to play passively then your path is a less dangerous one unless the other jungler invades in which you ping the lane closest to you for some help, hang back and jump on him. But if you're are playing passive then you will want to start whichever buff you please, red buff will make clearing your camps easier and blue buff will give you shorter cooldowns and energy regen which is nice for ganking. as soon as you have taken your buff move straight to the one you didnt to and take it to avoid any invading from the other jungler. then begin to take the smaller camps and when you have cleared your jungle you can gank the lanes that are pushing.

If you have a team with a lot of CC then this helps when you gank lanes. If your mid laner lands a stun, slow etc then you can Q onto them follow up with your E's slow and you will most likely pop a summoner or get a kill. Make sure you type in chat everytime you get a kill #lata, this will make the enemy flame while you laugh straight to the bank. Late game Lee Sin is incredibly good if you play him right, his mobility and chances to set up kills are endless. Easier said then done and it will require practice but if you find someone that is separated from their team it is funny and will secure a kill if you ward jump(even flash if you have to) and ult them into your team giving them the chance to jump onto him and kill. if you are alone and you want to stop the person from getting away sometimes its best to Q then and ward jump in front and kick them away and follow up with your Q, if you then follow up with your combo it will land a lot of damage on him.