Do not smoke. Do not light a match or do anything that might create sparks. Do not attempt to put out fires if a gas leak ignites. Call the Fire Department. In case of an earthquake or other emergency, everyone in your family should know where your gas meter is and how to turn off the gas.
Most meters are at the front or side of the house.
Some are put inside a building. In apartment or commercial buildings, they might be in the back. If an emergency arises and you don't smell or hear gas escaping, you probably don't need to shut off gas service. Locate the meter shut-off valve. It's usually the first fitting on the gas supply pipe coming out of the ground near your meter.