Cornmeal: Medium-grind gives a grittier texture, fine cornmeal makes a smoother crumb. I like something in between, so I pulse medium-grind in a coffee grinder for the perfect balance. Use medium for texture, fine for smoothness, or a mix of both.
Overbaking is the main cause of dry muffins, so check around 17 minutes, let the batter rest, and stir just until combined to keep them tender.
Important Note about Salt: Not all salts are made equal and cannot be substituted 1:1. If you are substituting table salt for kosher salt, you will need to cut the amount called for in the recipe by at least half.