Board game design basics: defining your goals, restrictions, the iterative design process, qualities of good games, taking feedback, and more (video):

https://www.youtube.com/watch?v=AAiCR1XVe68

This framework for thinking about the different stages of playtesting also helps you know what kinds of questions you should be asking testers each step of the way (video):

https://www.youtube.com/watch?v=MwxxlG8VGqk

Prototyping and playtesting: building a quick, testable version of your game, gathering feedback that matters, and iterating without losing momentum (video):

https://www.youtube.com/watch?v=gOysPDPiPII

You shouldn’t listen to every playtester suggestion, but how can you know which player ideas are worth considering? Here’s a process to help (video):

https://www.youtube.com/watch?v=uxvKT_yTLaQ

10 tips for making a better print-and-play version of your board game prototype for playtesters and publishers (video):

https://www.youtube.com/watch?v=u_Z3rGnXBQc