Keep Feet Dry. Perspiration is the underlying culprit. Techniques to keep feet dry would include: foot powder, absorbent socks (cotton/wool...Avoid synthetics like nylon, polyester). Changing socks and or shoes frequently helps. Aluminum chloride is a good topical aniperspirant found in underarm antiperspirant sprays. Some people will spray their feet before putting on socks. Prescription drysol can be used.
Also... Along with dr. Mitsos' excellent recommendations there is a small population that develop a special type of bacterial infection called pitted keratolysis. If the above suggestions don't seem to help the problem, check in with a specialist to see if this could be the underlying issue or if you may require more directed medical treatment for hyperhidrosis (excess perspiration).
Foot odor. The answers already given are great . I would only add hygiene and antibacterial soap and shoe spray like clean sweep . It usually takes more than just one thing to get rid of foot odor - and you must continue these steps to keep it in check .