If your building has a basement or other floor below ground-level subject to seepage or subsurface flooding, install drain tile and a sump pump.
If your building has a slab foundation, install a low floodwall, berm, or other barrier to keep water from reaching the building walls.
Install a floor drain plug, standpipe, overhead sewer, or backup valve to prevent sewer backups.
Elevate
and/or relocate electrical panel boxes, furnaces, water heaters, and
washers / dryers to a location less likely to be flooded.
Keep materials like sandbags, plywood, plastic sheetings, and lumber handy for emergency waterproofing.
If
flooding is likely, and time permits, move valuable / irreplaceable
items (photos, antiques, upholstered furniture, stuffed toys,
mattresses, etc.) that are most damaged by floodwaters up to a higher
level.