Thresh is primarily a support but excels at disrupting the enemy carry's farm by spamming Death Sentence followed by Flay.
You must perfect the timing of Dark Passage to save your allies. They can get shielded during fights and/or escape if needed.
You can help your team most by focussing your Thresh build on armor and magic resist. Thresh will often be the first to engage the enemy team during a teamfight. You will often be targetted; get enough tank to survive.
League of Legends Thresh players could find him to be a difficult champ to build out properly. You'll see that his build changes when he is playing against either generic or highly focused team compositions, meaning you shouldn't select the same Thresh build every single game of League of Legends
The most critical items to include in your champ's build are: Locket of the Iron Solari, Bulwark of the Mountain, and Vigilant Wardstone. Those who added these items in their builds had a better winrate than players who worked towards other Thresh builds. Similarly, if you are trying to beat a well-mixed enemy team comp, you should really consider grabbing yourself the Resolve, and Inspiration runes. In recent matches, he won the greatest fraction of his games when built with these runes.
We set our Thresh build suggestions by analyzing 168,851 recently ranked League games with him selected. We only advise the best winrate Thresh builds that have been built by ranked League players enough times for us to reccomend them. With so many matches in our data, we are confident in our recommended builds.