Do the boring work before the clouds show up. Clear leaves and debris from gutters, downspouts and private drains. Look for roof leaks, loose material and areas where water already tends to pool around the property.
Trim or secure vegetation and outdoor items that could become a problem in wind or heavy rain. Check that downspouts direct water away from foundations and walkways.
If your property has flooded before, do not wait for a warning to figure out where sandbags, barriers or pumps would go.
Official Resource
Ready.gov - Floods
Open Official Source