Early game you will want to rush a dorans and run bot,(best if you have a support/healer).

Check bushes with your teammate behind you,(if teammate a tank, stay behind with your skill shot ready).

Be rather aggressive trying to farm with your tempest/cripple.

Use initiating aggressive combo "Sonic Wave, resonating Strike, tempest, cripple".

If you are laning with a healer, recall less because you can stay in the fight, you are surprisingly powerfull.

Snowball very often to increase your income, you will need it.

As Lee Sin usually a jungler, you can EASILY solo dragon at around level 10, use this as an opportunistic time to support your team as an off jungler if there isn't one present.

Later levels try to "assassinate" or finish enemy champs below 50% health.

Use your CDR to an advantage, skill shot as often as possible, you don't even need to worry about mana!

Late game Lee Sin is very easily able to multi kill, depending on enemy, you will be able to solo 2-3 enemies with next to no problem.