Change the air filter in your central heat and air unit often, especially during peak usage months. Thirty days is the absolute longest you should ever leave an air filter in place; two weeks is maximum for high-usage months.
Using cheap fiberglass filters is actually, rather than the more more expensive HEPA filters because replacing the more expensive filters often isn’t cost-effective and the fiberglass filters actually allow for more air to flow into your climate-controlled unit, reducing the amount of energy needed to effectively heat or cool your home.