Keep your soap out of water when not in use.
Let your soap dry thoroughly after each use.
Keep your soap in a soap dish that allows for drainage.
I try to keep my soaps standing upright in the shower (of course I have a six soaps in the shower).
Most soaps are ready after four to six weeks of curing (water evaporates out of the soap bar) but soaps such as Castile (100% Olive Oil) Soap could take up to 10 months to fully cure so these soaps need to stay air dried after each use.