While you have some good suggestions already I'd suggest that, if you can afford it, you buy two pairs of shoes/boots that you alternate between. Wearing the same pair of shoes all day, every day doesn't give them time to dry out between wears. Investing in two pairs that you alternate will probably result in shoes that last much longer than two individual pairs. This is something I'm going to seriously consider next time I'm shopping for my "every-day" shoes.