Check the settings on your thermostat. Make sure the temperature control selector is set above the current room temperature, and the system switch is on the HEAT or AUTO position. The fan switch should be set to ON for continuous airflow or AUTO if you want the blower to operate only while the furnace is operating.
Try to get the furnace to turn on by raising the thermostat to its highest temperature setting.
If the air flow out of your registers seems low, check the air filter. An extremely dirty air filter can block air flow.
Make sure all registers are open and not obstructed.
Check the power disconnect switch by the furnace.
Check the fuse/breaker at the electrical panel for the furnace.
Check to make sure the gas control valve to the furnace is open.
Check the pilot light. (Electronic ignitions will not have a pilot light).