Your first step is obviously to find the source and shut it down, and make any necessary repairs. Next you want determine the extent of the damage. The best way to do this is with a moisture meter, but if you don’t have access to one of these, you can use the poke test. Take a sharp serrated kitchen knife and poke any drywall where water may have been. If the drywall comes out soft, or mushy, most likely it will have to be removed. Start at the lowest point and work your way up. Locate the the point where the drywall or plaster ceases to seem wet or soft. Good drywall should be dry and create a fine dust when cut. Drywall/plaster should be removed to this point, and any wet insulation must be removed. Often insulation may be saturated well above or beyond the wet drywall. After all wet material has been removed, you should set up a dehumidifier to remove as much moisture from the surround air as possible. This will speed up the drying process, and reduce the probability of mold growth. In extreme situations, you can turn the heat all the way up in combination with a large area dehumidifier which “cooks” the moisture out of the saturated materials. In less serious situations, a simple room fan, a box fan, or even turning up the air conditioning can greatly assist in the drying process. Anything to get the air moving. In addition, there are a variety of sprays that help remove mildew and mold, and help prevent future build up. Once all materials are completely dry, repairs can begin.
#1—deal with water intrusion source. #2 wet vac area, dry out asap, #3 placement of dehumidifiers / fans. Mold grows with moisture. If flooded room has baseboards, they need to be pulled…trapped water will mold. Any building product soaked with water must be treated / extremely dried within 48 hrs., #4, look for evidence of mold—blistered paint, black spots, or actual view…Mold is toxic when contained.
Carroll explained it well.
In a nutshell, get rid of any water left. Then, the key is air movement - lots of fans and dehumidifiers. Mold loves stagnant air and dark places , so open windows, get fans, etc.