Keep the store clean and stay polite!
An aspect I am always surprised by when shopping in Japan is that the stores are always impeccably clean! What I learned through experience is that the shoppers themselves leave the shops clean by folding the clothes or not picking up the clothes unless they like it.
Also, it is a Japanese custom in that the people respect other people. Japanese shoppers feel bad for leaving the clothes or stores dirty and therefore when trying on clothes, they fold or hang the clothes before giving it to the worker in the changing room. Therefore, when shopping in Japan, enjoy the cleanness of the stores and remember to leave the store clean by folding or hanging the clothes that you take!