Alright, I don't play a lot of Thresh, so take this with some salt, but I am a support main, and I play TONS of games against him - so I know what makes him tick.
**1.) Thresh is all about positioning and space control. **It's less about landing hooks and more about making the enemy aware that you CAN hook them. Make them afraid to stand infront of you and win the lane pressure without even trading - It's just like Blitzcrank.
2.) Throwing your Lantern out is a learned skill - and it's clear to notice the good thresh's from the bad ones on this ability alone. The best advice i can give here is throw it EARLY, and practice practice.
3.) Be careful about diving an enemy that you've just hooked - enemies can bait this really easy and get yourself killed.
4.) Most good Threshes won't initiate with the hook, infact, they will intiate with the small pull. Learn the distance well, it has surprising reach - if you can nab someone with it openly, it makes it VERY easy for you to land your hook on them after, and then its easy to control them.