Examples of source control include servicing combustion appliances regularly to decrease combustion emissions (e.g. carbon monoxide and nitrogen oxides), using low emission paints, varnishes, carpets, etc. in indoor environments, eliminating smoking indoors, keeping pets outside, maintaining low humidity, preventing moisture build-up indoors, cleaning surfaces regularly to reduce dust mite concentrations and mold growth, and eliminating excess debris from the inside of heating & AC / ductwork systems. These methods of source control are the primary control tactics for air pollution reduction indoors. Only source control can be totally effective at removing all pollutants from indoor environments.

Many of the above recommendations can be accomplished by the homeowner, e.g. purchasing / testing carbon monoxide detectors, radon kits, thorough cleaning. 

A more detailed action guide is provided by EPA's Asthma Home Environment Checklist.

Other recommendations are best accomplished by a professional service provider. Selection criteria is provided in the opposite column.