The BunnyFuFuu Way
Always get Pink Wards when possible
Protobelt for insane plays if ahead
Health to get Tanky
Extra armor against heavy AD
Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
The first thing I want to say about playing Thresh or support in general, is that you should always assume your ADC is a potato and cannot make plays. It is their job to cs, auto attack, and take the kills you serve up to them on a silver platter and sometimes not even that. The ADC can only auto and you have to completely set up the kills and make plays for them.
Introduction to Thresh
Thresh is a great champion to play due to his amazing kit, he has such high potential to set up kills and save the other plebs on the team when they're out of position.