If you must peek into the oven while something is cooking, purchase a model with a window. Each time you open the door, the temperature drops about 25 degrees. Preheat ovens only when necessary. Unless you are baking breads or pastries, you may not need to preheat the oven at all. Don't lay foils on racks.
Food cooks more quickly and efficiently in ovens when air can circulate freely.
Use glass or ceramic pans in ovens. You can turn the temperature down about 25 degrees and cook foods just as quickly. Use toaster ovens to cook small or medium-size meals. Check gaskets for good fit. When using gas, use a moderate flame and make sure the flame is blue.