Defrost your freezer. For manual defrost freezers, don't let ice build up more that 1/4 in. When this happens, the efficiency of the freezer drops significantly.
Check your freezer temperature. Keep your freezer at a temperature between 0-5° F. Settings below this use more energy and are not necessary.
Keep your freezer away from heat. Try to locate your freezer in a cooler part of the house. Make sure you keep it out of direct sunlight and away from appliances that generate heat like ovens and water heaters.
Close the refrigerator door. Opening the refrigerator door accounts for between $10 and $20 of a typical family's electrical bill each year based on 40-60 openings per day.
Inspect refrigerator door seals. Check the door seals on your refrigerator by closing the door on a dollar bill. If you can easily pull the dollar out then you would probably benefit by replacing the seal. The right seal for your refrigerator can be difficult to find, but you might try a refrigeration parts store.
Keep your refrigerator cool. Keep your refrigerator out of direct sunlight and in as cool a location as possible. Keep away from oven, stoves, water heaters, etc.
Keep the refrigerator level. If it is not level, the door might not close fully.
Keep refrigerator foods covered. Keep foods covered to prevent moisture build-up. Your refrigerator has to work harder if the air inside is humid.
Reduce the load. Refrigerators operate most efficiently when full but not overloaded.
Don't put hot food in the refrigerator. Allow leftovers to cool before putting in the refrigerator.
Give your refrigerator some space. Allow at least one inch of space on each side of the refrigerator for good circulation. Poor circulation can increase energy consumption by 10%.
Turn off moisture control when not needed. If your refrigerator has a moisture control switch ("anti-sweat" heater) you can generally safely turn it off on all but the hottest days (and even then if you have central air), and reduce the energy cost of your refrigerator by about 10%.
Clean the cooling coils. Vacuum behind your refrigerator at least once a year, making sure to remove dirt and dust from the coils. Dust build-up not only increases energy use, but it may cause the unit to break down. (Some refrigerators have the coils inside or underneath where you can't get at them. Most built-in models have them readily accessible on top, typically behind a removable grille).
Turn off spare refrigerators. An older second refrigerator consumes a significant amount of energy: it could be costing you over $200 per year! Perhaps you can get all your food into one refrigerator and turn the other off permanently.