Unless you are baking pastries or breads, you may not need to preheat at all. Try to avoid opening the oven door a lot as you cook . Each time the door is opened, a significant amount of heat escapes. As a result, food takes longer to cook and you waste energy. Instead, use your oven light and inspect through the oven door window.
Foods cook more quickly and more efficiently in ovens when air can circulate freely.
Do not lay foil on racks. If it is possible, stagger pans on upper and lower racks to improve air flow if you are baking more than one pan at a time . Cook double portions when using your oven, and refrigerate or freeze half for another meal . Use glass or ceramic pans in ovens. You can turn down the temperature about 25 degrees and cook foods just as quickly.