Keep the Humidity Low
In basements, you can keep a dehumidifier running at all times to keep the moisture out of the room and the humidity level low, which prevents mold spores from clinging to walls and carpeting. Because basements are underground, the air has a tendency to stay moist a good portion of the time.
Dehumidifiers run about $100 and can be found at your local hardware store. They don't take up much space, and they are relatively quiet while running. It is also recommended it be ran in a central location in the room to evenly keep moisture out of the air.
In bathrooms, consider installing a vent fan (if you don't have one already) and run the vent during baths and showers, and keep it running for at least 15 minutes afterward. You can also open a window to help with ventilating the room, provided it's not too cold outside. Also keep the door open to circulate the air.
Clean the Molded Surface
First, wear gloves and cover your mouth and nose before touching mold. Spray the moldy surface with a mixture of bleach and borate. Let the solution soak for several minutes. This kills the mold. If the mold has accumulated on a rough surface, such as a concrete wall, it may require some scrubbing, so be sure to have a brush or some other type of scrubbing tool on hand.
Completely Remove the Molded Surface
If mold has accumulated on drywall or wood and cannot be removed by thoroughly cleaning the area, complete removal of the surface may be required. If mold has saturated through drywall, locate the entire area it has affected and cut the drywall out. If you aren't sure how to approach this, you may want to consider consulting with a mold specialist. Mold can vary in colors, from white to green to black, and can also present itself as mushroom-like. When mold has gotten this bad, it may be time to turn to a professional.
Fix the Source of What's Causing the Mold
Sometimes humidity alone isn't the only cause of mold. If you have water constantly leaking into your house, for example, from cracks in the foundation, flooring or walls, a leaky roof or defective plumbing, these will need to be repaired so you do not keep experiencing problems. If you are not sure what is causing the mold or are having difficulty isolating the problem, the best thing to do would be to consult with a mold-testing professional. Also, if you have a large area that has been affected with mold, consider hiring a mold professional. Mold can be very dangerous and can cause sickness and allergy troubles, and when it's a big problem it's best to be handled by someone who specializes in its removal.