I’ve made quite a few dud threads.
The most popular thread I created was asking people how they came up with their username.
So just based on my own personal experience a thread that garners maximum participation is one in which everyone can participate in (having a username we each came up with is something we all have in common) while simultaneously being interesting to everyone that reads it, and encourages others to participate because it’s fun.
This thread wasn’t even that big, but it was my biggest