Hi!
Atm i'm g1 support. Thresh is champion that I play mostly (about 90 of 130 ranked games this seson). I played all supports but noone gives me as much fun as thresh. I tried much builds, much masteries and runes. It's the best build for me and i play with it mostly.

If you have only ap or ad runes check notes above runes. On marks you can play armor too. If you have no ip you can play hp on quints and armor on seals byt it gives you worse statisticks.

All is in notes above masteries.

If you can't lasthit minion or just don't like relict shield (or like coin) you can buy coin. I tried spelltieth vs morgana. How does it work? Take ap runes, ap 9/0/21 masteries, max hook and if morgana shield someone you are able to broke her shield with your hook and then go in with 2nd q use to use som cc like e and r. You must collect much souls to have enough ap to broke shield.

I ussually max e 3 times to have poke with basic attacks. Then i like to max lantern. Most of ppl max hook. I don't think it's bad idea. If u prefer max hook and can engage more often go ahead.

It's easy: exhoust is good most of times. If u prefer risky option take ignite which can give you some kills but won't stop fat carry or help peel your carry or if u think that exhoust isn't good (it's hard to exhoust caitlyn cayse u have no range to do it or enemy team have no good targets for exhoust).

You are really strong at level 2. Start with Flay and just attack minions to kill them faster than your opponents and hit 2nd lvl faster. if enemy botlane have still 1st lvl and you'll connect your hook it's easy kill or burned spells what means that u can easlier kill them in future. Don't forget about your basic attacks which are really strong cause u have ad in runes and masteries. Make enemy adc can't farm by harrasing him when he want to last hit. U can call your mate to freeze lane next to your turret and zone enemies (stay between minions and them and don't let them to come closer. If your adc knows what is he playing u can call him to be careful and roam mid. If you see jungler fighting in bottom jungle you should go and help him too. DON'T FORGET ABOUT VISION!

Thresh is very universal champion. Most of times you have to catch someone and engage and then peel your carry. But you can do other roles: engage when your carry isn't focused in fights (just try to hook any soft enemy and follow with 2nd q, e and r. then try to stay far from your carry and reposition him by lantern), peel when your team have good engage or when your adc is focused (stay close to your adc and cc all enemies that want to kill him. You can also reposition him with your lantern), disengage when your team is behing and you don't want to fight (just use r between both teams to slow them and buy some time to get far from enemies), you can try to be frontline but it's not really good. DON'T FORGET ABOUT YOUR RELICT AND MIKAEL!