Season all your new baking pans by applying a very thin coat of vegetable oil and baking empty for about 25 minutes at 400 degrees. A very thin coating of all-purpose shortening will cause muffins to release. Apply the shortening to your muffin pans, but also dust the cups with a thin coating of bread type flour for good release. Heavy steel pans are best for baking muffins. Light weight pans may cause the crust to brown before the middle is done.
Most ovens have a tendency to have hot spots.
Always place your muffin pan in the middle of the center shelf. Muffins need a 375 to 385 degree temperature to bake properly. Make sure your oven temperature setting is correct. Test for doneness by touching the center of the muffin. The center should feel firm to the touch and spring back to a soft push.