Hi, my IGN is Bistru and I am on NA server. Currently a Silver V player,(yup, elo hell never ends.) I have played thresh as my to go support for awhile and had made some good plays in my games. I've seen many new thresh players struggling in certain ways to play or build thresh. And this is my guide, I constructed with my experience and from builds i've seen from many other players. If you like my Guide, plz share some love and share it. ༼ つ ◕_◕ ༽つ Enjoy !

[*] good initiation
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[*] good lane pressure
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[*] nice autoattack range
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[*] good disengage
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[*] good slow with box

protection with lantern and flay

[*] Hard to master
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[*] Counters by hard cc

Depending on my ad carry, I'll be very aggressive in lane. I bring ignite so as soon as I hit lv2 I go straight on either the support or the carry. The ignite can either burn out a flash or kill them. ☜(⌒▽⌒)☞ Make sure to toss a lantern near the river or beside your turret for your jungler or ad carry to follow up.

When in lane don't be afraid of flash flaying or hooking. This technique could let your adc become fed and could even win your lane within few minutes of the game.
As for team fight you basically lay down your box and flay enemies either away or into your team. When initiating, you could hook someone on their team , then flash flay the carries backwards and your team could do a easy follow up team fight.
( ﾟヮﾟ)

There is not much to say about thresh's late or mid game. Thresh is extremely OP if played correctly and all you really have to do to get better is practice and play with someone you have good synergy with.
AND ALWAYS UPGRADE YOUR TRINKET !!!! ┻━┻ ︵ヽ(`Д´)ﾉ︵ ┻━┻