Weather-strip, or use door sweeps around doors, windows and anywhere a draft is felt. Fix or seal broken or cracked windows, especially in the basement. Patch or caulk holes in floors, ceilings and walls. Close off heat escapes like fireplace dampers when there's no fire, checking to make sure the seal is tight, and limit use of kitchen and bathroom fans. Install rubber insulation gaskets in outlets and switches.
Fireplaces provide heat but also suck it off at great loss.
Use glass doors and fan-powered heat exchanger that recirculates hot air back into the room. Clean and repair all furnace and heat pump filters monthly. Fix broken ducts and replace cracked or peeling tape. Set refrigerators between 37 and 40 degrees Fahrenheit. Vacuum or brush the cooling coils at least every six months, and check door gaskets.