Wear gloves, an N95 mask, and eye protection
Open windows and improve ventilation
Fix the source of moisture or leak first
Remove and discard any wet or moldy porous materials that cannot be cleaned
Clean non-porous walls with soap and water
Scrub visible mold with a mold cleaner or a solution of 1 cup bleach per 1 gallon of water
Never mix bleach with ammonia or other cleaners
Rinse the area with clean water if needed
Dry the wall completely with fans or a dehumidifier
Keep indoor humidity below 50%
Repaint only after the wall is fully dry
Replace damaged drywall or insulation if mold has penetrated deeply
Call a professional if the mold covers a large area or keeps returning