Use an exhaust fan to circulate air. Don t leave damp clothes, towels, etc. in hamper. Seal cracks in the walls or floors. Use a dehumidifier. Good ventilation and lighting discourage mold growth.
Houseplants provide a haven for molds.
Crushed rock on top of the soil around each plant will reduce the number of mold spores entering the air. If problems continue, you may need to give the plants away. In summer, keep them outdoors. Mattresses and other bedding sometimes become mold-infested. You can usually discourage mold growth by frequently washing the bed clothes.