Shoe etiquette is extremely important.
House slippers are the norm in Japan — before entering most homes, the hosts will ask you to take off your shoes and offer you a pair of house slippers. In fact, separate pairs of slippers are often worn in bathrooms and public spaces.
You might even witness this custom when you tour historic sites (especially holy places) and restaurants, which might have you dine on a raised tatami platform. This is one rule you won't want to break, so look around and do as the locals do.