Remove dampness from the air with an air conditioner and/or dehumidifier.
Use bleach or fungicide (mold-killing cleaner) to clean all areas where water regularly collects, such as in drip pans (from refrigerators for example), dehumidifiers, humidifiers, and showers.
Run the bathroom vent while showering to remove excess moisture from the air. (Make sure bathroom vents exit the house properly. Improperly positioned vents may put moisture into the attic or walls, increasing mold growth.)
Dry clothes before putting them away.
Open shades during the day to let in sunlight.