The best way to ensure good indoor air quality and a safe and healthy home is to prevent air quality from becoming bad in the first place. This comes down to either blocking the entry of the contaminants and moisture or removing existing noxious materials substances, and properly venting sources of moisture. Some options cost little or nothing, like discarding expired or unneeded paints and solvents, or sealing air leaks between indoors and outdoors and between occupied spaces and crawl spaces and the garage. Some options can be quite costly, like removing mold and removing or containing asbestos.
Some types of contaminants—particularly VOCs, particulates and microbes—can often be effectively removed or reduced by filtration. This can be as simple as buying a high-quality filtration system for your heating system or a free-standing electronic filter.
Flushing contaminants and moisture by ventilation can also be an effective strategy. Spot ventilation in kitchen and bathrooms can remove moisture and particulates from cooking.
A dehumidifier removes moisture from the air and can help prevent the growth of microbial contaminants. It can also increase comfort on muggy days. Heating systems can dry out the air significantly. This can sometimes make skin or respiratory ailments worse. A humidifier can help relieve those ailments.