One tip I didn't mention in the article is to include a ticking clock. Seth Skorkowsky discusses this (and lots of other useful tips) here: https://youtu.be/2VRy5nNK_So?si=PS0PnaHSxrLLsTmm. It's also important to distinguish between mysteries in RPGs vs. mysteries in traditional storyelling. I try to avoid thinking in terms of "plot" or "narrative" in favor of "situations" and "potential events." Preparing the latter provides tools to improvise without requiring a linear plot. The narrative that ultimately emerges is a matter of the players' choices. How exciting, engaging, and satisfying that narrative is comes down in large part to how much agency the players have in directing it. So, the general GM advice on supporting player agency applies to mysteries, too.