Wash feet, scrub them with soap and water, rinse well and pat dry before donning socks.
Buy socks with high cotton content (80% or better) and throw all your nylon socks in the trash. I'm serious, socks with high nylon (or other synthetic fiber like rayon) will make your feet sweat and smell sour. Why I don't know, but they do.
Launder shoes and/or inserts well. Wearing old nasty fungus ridden shoes will just reintroduce odor-promoting microbes to your socks and feet again. Wear shoes that allow some air exchange.
Buy a big container of antifungal/bacterial foot powder. Sprinkle a little in your socks before donning and a little dabble in your shoes.
If necessary, bring a fresh change of socks to work/school and change mid-day.
After a week or two of doing this, you'll see a huge difference. Foot care is something you want to do as you go, because an ounce of prevention is certainly worth a pound of cure where your feet are concerned.