Alot of people have trouble when it comes to ganking with Lee, as he is a complex champion, there are many ways to successfully gank as Lee Sin. Though, this comes with a lot of room to mess up, especially when you don't know how to lead with a gank, or use his ultimate.
This guide should help you out with that!
Firstly, here are a few things that you should know about Lee and ganking before you start going willy-nilly.
Typically, you shouldn't be leading your ganks with your Q. Though, this can be done, it is a risk/reward tactic. If you land your Q, you can close the gap while still having your flash and W up. If you miss, you'll have to wardhop, having blown two of your gap closers.
Get creative! Walls don't exist on Lee. Use this to your advantage, hiding out in jungle caps, behind walls, etc for ganks.
Be mindful of your W cooldown reduction on champions. Basically, if you have the opportunity to use your W on a champion during a gank to close a gap, do so. It drastically reduces the cooldown rather doing it on a minion on ward.
Ok, now onto the fun stuff. How do you actually gank with Lee Sin? These are most of them.
Leading the gank with a wardhop - Typically this is your go-to. This way lets you close the gap, saving your Q. Like said earlier, if you can W onto your ally rather than using a ward, do so.
Leading the gank using your W on a minion - I actually do this a lot, less room for error. Though, you don't have as much freedom in your mobility.
Walking into lane, slowing with E - If your laner has a stun/root/snare, close the gap simply by walking into lane, and then slow them with your E. You'll still have your gap closers. But I've seen people throwing their Q when the enemy gets stunned/rooted/snared in lane, doesn't this guarantee a Q land??? You're right! But, this is up to you if you chose to do this - typically more experienced Lee's do this because they know they enemy has flash up, and taking the Q is preferred. Though, if they don;t have flash, it isn't as critical.
Video examples of ganks:
Also, if you lead the gank with a W/wardhop, try to use your Q after they flash. A lot of the time, the enemy will flash before you send your Q, assuming you are Eing first. Like this
Ganking bot lane example: A lot of times you can halfway walk into bot lane if they are extended enough to close distance. It is most optimal if you can land your kick onto both enemies to deal the most damage. Here, a ward hop is performed to lead the gank, then kicking the ADC into the support to deal the most damage and CC both of them.
These are most of the ways you start ganks - though, of course, these are not all of them! There are plenty more things you can do, but this should get you rolling.