Replace worn weather stripping and caulk. Replace old windows or install plastic window seal. Attach draft stoppers to doors. Hire a contractor to perform blower test to find leaks. Install foam gaskets behind wall switch plates. Close fireplace damper when not in use. Close crawlspace vents in summer and winter.
Hire professionals to clean, check system. Replace air filters monthly. Use a setback thermostat. In winter, set ceiling fans to blow upward.
Check for adequate insulation floor, wall, and ceiling.
Trim trees. Clean gutters. Install chimney screen to block leaves. Keep snow, ice away from garage door. Check condition of steps and rails. Drain gasoline from lawn mowers.