Preheat oven to 350°F. Cook and drain the shells, being careful not to overcook. Spread half of the tomato sauce and the mozzarella in a baking dish (I usually have to use 2!) Mix the beef and the sausage in a large mixing bowl. Add a dash of salt and pepper, the parmesan cheese, and any seasonings desired.
Stuff the manicotti shells with the mixture and place in the dish. Cover with the remaining sauce and mozzarella cheese.
Cover with foil and bake for 30 minutes. After 30 minutes, remove the foil and bake for another 10-20.