Close them at night to help keep out the cold. The broiler needs preheating only for rare steaks. Poor air flow can cause uneven baking. On top burners use the smallest flame possible. The flame should never exceed the pan's width.
Water boils faster in covered pans.
Avoid overcooking, which reduces nutritional value. If the burner flame is yellowish instead of blue, clean the burner with soap and water. A blue flame is more efficient than a yellow one. Some aerosols, such as nonstick cooking sprays, may cause the flame to appear yellow. Also, avoid running hot water unnecessarily during hand washing or shaving.