What is the best way to clean indoor air the lifehacker way?
That is, excluding store-bought air purifiers of expensive brands.
Something like DIY: Building an energy efficient and low cost filter would count if construction plans/ideas and maintenance costs were to be considered.
It's mainly about particles and dust from burning candles, incense, tobacco, but also the usual dirt and inner city pollution from roads and vehicles, humans, pets, pollen. Some of that is not easily avoided. Odours are much less of a concern.
Vacuum cleaners with good filters should be considered a given. But they use huge a mounts of electricity if left turned on for long, just cleaning the air and not only carpets.
Structural alterations like plastering the walls of an apartment are not feasible.
Plants are nice and effective according to NASA, but already present and not really cutting it.