Maintain comfortable but not too high temperatures when setting your thermostat while heating.  Increase settings during the winter but keep in mind to monitor the level to avoid continuously high gas bills.

Install a programmable thermostat that adjusts the temperature automatically.

Check furnace filter periodically.

During the winter open drapes and blinds to allow for the sunlight to help heat the house during the day. Close drapes and blinds at night to reduce the cold air coming in through windows and doors.

Be sure that heating and cooling vents are not blocked by furniture and/or draperies.

Wash laundry with milder water instead of hot water.  By adjusting settings on washer, less gas  will be needed for the desired water temperatures.

Reduce shower length, allowing less hot water to be used. 

The above also holds true for dishwashers.  Avoid washing half loads when washing dishes.

Position the freezer and refrigerator away from cooking area as much as possible.  Also try to keep refrigerator and freezer full.

Clean lint from dryer regularly.

Consider replacing any gas appliances that are more than 10-12 years old.

Check insulation levels where possible. Insulation levels in the attick can easily be seen. Insulation in the walls are more difficult to detect.