Sealing and Insulation

Seal from the inside. Seal gaps and holes in walls, floors, and ceilings with caulk or foam sealant. Look for cracks around windows and where wires and pipes pass through.
Caulk along baseboards with a clear sealant.
Caulk around openings where water and drain lines through walls underneath bathroom and kitchen sinks.
Caulk electrical wire openings at the top of the interior walls in the attic.
Ensure windows and doors are properly weather-stripped and use door sweeps.
Ensure window A/C unites are weather-stripped.
Caulk around storm windows and basement windows.

Have your duct work checked for leaks. Leaks at the return, air handler and supply can be a major source of high bills. For mobile homes, check for leaks at the grill, cross over duct and down flow air handler.
Ensure attic access door closes tightly and is insulated.
Make sure insulation in your attic does not block soffit vents.
Verify your ducts are tightly connected to your HVAC equipment. Well-sealed and insulated ducts can save up to 10%.
Insulate electric wall outlets and wall switches with foam pads.