Put a plastic cover over dirt in crawl spaces to prevent moisture from coming in from the ground. If there is standing water or the soil is wet, dry it out with fans before covering the floor.
Be sure crawl spaces are well ventilated by using fans and having vents installed in outside walls if necessary.
Consider painting concrete floors and using area rugs instead of wall-to-wall carpet in basements. If you plan to install carpet over a concrete floor, it may be necessary to use a vapor barrier (plastic sheeting) over the concrete and cover that with sub-flooring (insulation covered with plywood) to prevent a moisture problem.
Have your basement floor checked for leaks and have them repaired if necessary. Water can enter your home by leaking or by seeping through basement floors or walls.
Make sure gutters are working properly and that outdoor landscaping causes water to run away from -- not toward -- the house.
Do not finish basement walls with insulation and wall board unless your basement is very dry.
In the laundry room:
Vent your clothes dryer to the outside.
Make sure the vent is clear of obstructions, such as lint, and that there are no holes that leak air. If the vent duct is damaged, replace it with a metal duct. Have the duct cleaned at least once a year.
Avoid leaving damp clothes in the laundry basket or dryer. Wash and dry them promptly.
Use exhaust fans to remove moisture to the outside (not into the attic).
Use area rugs, which can be taken up and washed often instead of wall-to-wall carpeting.
Check for leaks around basins and tubs and have them repaired if necessary.
Open a window when showering.
Avoid leaving damp towels on the floor or in laundry hamper.