Use soap and water to wash your feet, and dry well, including between toes. Trim your toenails -- straight across -- to keep them shorter than the end of your toe. Make sure the tools you use are clean, too. Wash clippers and files with soap and water, then wipe with rubbing alcohol. You might be tempted to cover up discolored nails with polish, but don't. Your nail bed can't "breathe," which keeps fungus from going away.