The first step:
The first step towards better air quality can already be reached with proper ventilation. This will guarantee a continuous supply of fresh air from outside and expels the polluted air from your house. The air quality outside is usually better than the air indoors. Everything that has accumulated in your home and all particulate matter that you produce inside, for example by cooking, is exchanged in this way.
But of course we want to prevent other substances within the fresh air from entering the house again. Because, as I just said: pure air is better air. How much substance enters depends very much on the environment. Each area has its own characteristics that influence the air quality. This can have human and natural causes. Traffic, industry and livestock can emit a lot of particulate matter, but this is also released from agriculture and, for example, in nature reserves along the coast. There are several websites available where you can find the air quality in your area. And once you know that and are aware, you can also take the right measures.