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.
Mix 1 tbsp of hydrogen peroxide with 2tbsp of baking soda to create a paste. Use a cotton swab to apply the mixture to the nails and underneath the nails. Leave it on for 2-3 mins and rinse off with warm water. Baking soda will naturally exfoliate the nails while the hydrogen peroxide will brighten and whiten them.