Wash your feet daily in warm water with mild soap. Dry them thoroughly.
Dust your feet with baby powder, or nonmedicated foot powder. An antibacterial ointment could work, too.
Change your socks and shoes at least once a day.
Wear shoes that let your feet breathe: leather, canvas, and mesh are good options.
Avoid wearing the same shoes 2 days in a row.
Soak your feet in strong black tea (two tea bags per pint of water, boiled for 15 minutes and mixed with 2 quarts of cool water) 30 minutes a day for a week. Or use a solution of one part vinegar and two parts water.