Human pathogenic fungi usually dwell in the thickened layer of horny (keratinized) epithelial tissues; that is why it makes sense to get rid of all possible “refuges” for fungi. Regularly remove all callosities from your feet with pedicure file or pumice stone.
Wash your feet every day. After that, smear them with a body cream containing antiseptic and antiallergic agents. The cream would form an oily film on your skin, which would be impenetrable by fungi.
Never put on someone else`s shoes, nobody would tell you that he is suffer from toe-nail fungus. However, if you have tried someone`s shoes, wash your feet and wipe them and your shoes with a piece of cotton wetted with alcohol as soon as you are home.