What resources have been invaluable to you for having early customer conversations?

Hey, Indie Hackers fam would love your feedback. I built https://yourhundred.com (it's like tough mudder meets early customer discovery). As part of this, I'm compiling a database of resources (Blog posts, youtube videos, and other pieces of content) about doing effective outreach for early customer conversations. This is a really dope group, so instead of doing a google search (and seeing the most search optimized results), I wanted to ask y'all what resources you've come across that have been invaluable in your journey. Thanks!