Wipe down the shower stall after every use until dry, and clean it regularly with bleach. Since shower curtains are also prone to develop patches of mold, wash them at regular intervals with a good detergent. Use a solution with vinegar in it for the final rinse. If you are uncomfortable using bleach, vinegar works well as a substitute. Finally, this fungus flourishes in the dark, so ensure that the shower area is brightly-lit.