When it comes to your home heating furnace, dirt is the biggest problem that causes most heaters to run inefficient or fail. Dirt will effect three components in your furnace, the motor, the blower and the filter system. Let us start with the furnace filter. The filter should be cleaned or replaced before the beginning of the heating season. Then depending on the amount of use it will get during those cold winter months it should be checked and cleaned once a month. In order to check the filter you will need to remove it from the heater and hold it up towards the light. If you cannot see light coming through the filter it is clogged and will need to be replaced. If you are using a disposable filter in your furnace you can look on the side of filter and the size of the filter will be printed on the frame. When replacing the filter make sure and check to see the arrow on the filter is pointing in the correct direction. The air flows from the return air duct and towards the heater, so the arrow will be pointing towards the heater and away from the return air duct. If you are using a cleanable air filter simply rinse it off and let it dry before reinstalling it.
Next we will want to look at cleaning your blower assembly and the housing of the motor. If your furnace is designed with a squirrel cage type fan you will want to close attention to cleaning the openings since they are easy clogged with dirt and will make your furnace run less efficient. In order to clean the blower you will need to take off the panel that covers the filter. This will give you access to the panel or blower on the front side of the furnace. Once you have access to the blower unit, it can be removed by unscrewing a few screws from the blower and slide it out. You now can clean the assembly and reinstall it. If this scope of work is beyond your capabilities, then you should look for a qualified heating repair company that can do the work for you.