Replace air filters - A dirty furnace filter will block the flow of air and will slow down heat movement throughout the house.
Clean air vents - Similar to a dirty filter, dust builup in floor vents can block air flow and prevent heat from moving freely.
Cover/Insulate exposed piping - Uninsulated piping from your furnace or water heater allows the heat to escape easily and will cause those systems to have to work harder to generate the desired level of heat.
Check for holes or cracks on the outside of your home - Often times the foundation and siding of a house can become cracked, which allows air to flow in and out of the house.
Check your windows and doors - Insufficient window and door seals are a major cause of heat loss; however, this problem can easily be fixed with sealant or caulk.