[tuatoru]

Ideally, at least two pairs a day. Socks with silver-impregnated threads may help, for example Silverlight Hiking Socks. Silver is reportedly antibacterial.

Wash your insoles or replace them with fresh new antibacterial ones. Lift your insoles out of your shoes when you take them off, and air out the insoles and shoes, outdoors, in sunshine if possible.

Wash your shoes in a washing machine with laundry detergent if they're synthetic, otherwise swabbing them out with dilute acetic acid (diluted vinegar) may help. Right now, and weekly from now on.

(This question is a mild obsession for the "through hiking" crowd. Although they usually wear the same socks for a week at a time--but have separate socks and shoes for use at camp, while the hiking socks, shoes and insoles air out.)