So this is the way I play Lee Sin. I have taken things from many other people to get this knowledge. Enjoy!

Super Pros

Awesome damage
Awesome ganks
Awesome CC with Ukti
Tanky-ish
Is Asian. Bruce Lee FTW

Evil Cons

Damage late game is not good as others such has Riven
Needs better pants
Takes some skill (easy if you can land q)

6 Desolation Marks And 3 Flat damage marks to help you in jungle and give penetration against champions with armor.

9 Flat Armor Seals to help you in jungle greatly.

9 Per level Magic Resist as Lee Sin is vulnerable to magic.

The 2 Desolation and 1 Strength Quintessences is for same reason as marks.

- Your core jungling item. It is a must have early / mid game. The passive makes you amazing at clearing camps and the early damage, armor and lifesteal benefits you greatly. However, sell it later in the game for a bloodthirster for extra damage and lifesteal.
- These boots are probably the best boots for Lee Sin, but arguably, it can be the best boots for anyone. The build lacks Mres early on, so it is very useful. Also, the 35 tenacity is just wayyyy to good to ignore.
- This is great on anyone. ANYONE. but for Lee Sin, it is a core item because all the stats benefit him greatly and the slow and 150% damage proc is amazing. This gives him Move Speed for chasing, AD, attack speed, and crit chance for damage, hp for sustain, and the passives for his bursty abilities. Overall, its a great item. Get it.
- This item is great. It lets you be tanky, but gives you damage at the same time. I've heard complaints that its even "OP". Ever though you dont have a lot of HP after a phage, it is a very nice item to get. The armor is great and the crit chance is good with the crit you get from trinity later on. People always think "Oh if I dont have like 3k health its not worth it." But that isnt true. With around 2k health at this point, you gain about an additional 40 damage. thats like a bf sword that gives you armor and crit chance. Also, as the game progresses and you get more items, you will end up with around 3.5k health, and thats around 70 bonus damage.

- This is what makes you very tanky and gives you a great atma's boost. I get it regardless of what the enemy team comp is, because health always helps. At this point, you should get kills and assists easily, allowing you to stack the warmogs' passive quickly. If you think that you are too squishy, and the early Atma's Impaler won't help, you can always get this item first to become very tanky earlier.

Thanks to Listen to their Heartbeat Lee Sin guide. Saved me a bunch of time!

As Lee Sin you want to give your carries your kills. ALWAYS! Though you can get the kills when the carry isn't near. hehehehehehe

Some tricks to use as Lee sin are....

Use wards to jump too.
Q then Ulti then Q to have lot of burst damage
Kick Enemy into team and do not use it as a finisher
Use e and q to see invisible enemies.

Ok so hope you do well and give me some comments below.

P.S. Forgot to put in why summoner spells.

Just use Smite as you jungle faster and Use flash to initiate and get away. Bye!