My students often pronounce the word "clothes" with two "s" sounds. They think it sounds the same as "closes". I write CLOTHES, CLOSES, CLOSE on the board and explain the difference. They are always surprised.
Another difficult thing for Japanese is putting the "d" at the end of close. It seems that if something is not open here, it must be close. I say no, no, no - if it is not open, it is closeD.