The most important aspect of preparing for a flood is the mold damage, Mold can get in to most any porous surface, including the wood studs and joists in your home.
Toxic mold can grow within a 24-48 hour time frame after exposure to water, and can typically only be removed by disposing of the affected areas. Mold itself, if left to grow in your home, can cause a series of problems, including upper respiratory problems, irritation in the eyes, nose, and throat, and issues with the central nervous system.
When a flood hits, you are going to need a company that can remove mold and remediate the affected areas to stop the potential spread of mold and the continued contamination of your home. In normal cases, this means that any affected area will need to be removed (including wet wood, flooring, and drywall material).
With this being said, cleaning up mold should not be a DIY job. There are businesses that specialize in mold remediation, including companies that deal with the affected areas as part of their business model (carpet cleaners, for example). If you try to clean up mold yourself, then you risk leaving mold behind to continue to spread over months and years, and you risk exposing you and your family to additional toxic spore.