Not preheating the oven
You’ve probably read that you should preheat your oven to 350°F before placing anything in the oven. This isn’t something that you want to skip. If you pop something in the oven before it has had time to preheat, it won’t just heat up unevenly, but it’ll also time almost twice as long to bake to perfection.
Also, preheating the oven means turning the oven at 75° higher than the recipe calls for. Wait for between 30 and 45 minutes (hopefully, you’re prepping your food or letting it rest right now) before placing the baking dish inside of the oven. When you do, as soon as you close the oven door, lower to temp to 350°.