Ventilation matters more than most homeowners realize. Bathroom and kitchen fans should run during and after showers or cooking, and they need to vent outside rather than into the attic. Attics and crawl spaces need airflow of their own, too. A crawl space that's sealed up without a vapor barrier can trap moisture instead of keeping it out.
A dehumidifier is one of the better investments for a coastal home. Running one in a crawl space, basement, or a room that stays closed up keeps humidity below the level mold needs to grow, especially through the summer months. Check it regularly. Once the tank fills, it stops doing anything.
Leaks matter even more. A slow drip under a sink, a cracked pipe, or a roof leak after a storm can soak wood and drywall for weeks before it shows on the surface. Fixing a leak within a day or two, rather than letting it wait, is one of the cheapest ways to avoid a much larger repair later. Crawl spaces deserve a regular look too. Standing water, damp insulation, or a musty smell down there often shows up before any sign reaches the rooms above.