Daily washing of the feet with soap and water or quality anti-fungal soap; drying carefully, especially between the toes; and changing shoes and socks regularly to decrease moisture. Reduce perspiration by using foot powder in shoes, and wear shoes of leather or canvas, or perhaps nylon mesh, which allow good air circulation. Avoid walking barefoot and use shower shoes whenever possible. The same fungus that causes athlete's foot can also infect the toenails.
If you have yellow toenails or other toenail fungus symptoms, you may want to read Dr. Hurless' recommendations for treating toenail fungus.