When making a casserole, it's best to follow the recipe's recommended dish size and material. Only fill the dish 3/4 of the way to stop it from overflowing.
If you don't drain cooked meat, its fats and juices can make a casserole watery and greasy. However, you don't have to do this with very lean proteins.
Using a metal baking dish can add a metallic taste to your casserole and make it cool too fast, so it's lukewarm before you even get a chance to serve it.