This build and play style is meant for experienced thresh players
*also this is my first build*

ADC Thresh is an odd adc and in early game where you don't output much damage you need a support who can make a 2 v 2 into a 1 v 2(separate the adc from their support). Champs like Blitzcrank or Nautilus. They work well with Thresh in many ways.

In early game you need to get you and your support to your lane early. Once you and say Blitzcrank are set up in the bush your team combo should be: Blitz pull- Thresh pull- Thresh Qs to enemy Champ- Ignite- end. This makes your lane have a massive lane dominance because this separates your two lanning enemies making it hard for them to recover. Now you farm by last hitting mobs with your q's passive.
Once your push up to your enemy's turret you have two options
A. Gank mid while you let bot get pushed.
B. Use the lantern Blitz combo ( NOTE THIS ONLY WORKS WITH BLITZ ). As blitz goes in for a turret dive you throw down your lantern. As Blitz shoots his Qs he clicks on your lantern dragging him into safety and also dragging the selected enemy to you ( This creates a massive distance gap between the two enemy champs).

Mid game is simple. Gank often with blitz and don't always be hero. Many times when i play as thresh i feel the need to save my team, but remember DON'T PUT YOURSELF INTO HARM. Use your lantern or ulty to save team but never qq to a 5 v 5 with out tank starting the fight. YOU WILL DIE NO MATTER HOW FED YOU ARE. Another thing to remember is that thresh is weak to magic damage so target the APC. APCs are your worst nightmare and need to be taken out before you can rush in.

At this point you should do massive basic hits. Stick with your team. Grab baron, and dragon you know the whole late game deal.
Also you can 1 v 1 almost anyone no matter what even if your 1/4 of your max hp just let you q's passive fully charge up and then hit. The massive amount of damage you do will most likely make the enemy run away.