DEAR MISS MANNERS: What is the proper etiquette regarding bedroom assignments for guests? A friend of mine told me that it is good manners to offer the main suite to guests, especially married and/or elderly couples. I was never advised of such a rule when I was growing up, and I wonder if I have been impolite over the years. My adult daughter, her boyfriend and his parents — who live out of state, and whom I have not yet met — will soon visit me. They will drive several hours for us all to have dinner together, and then stay at my home for one night. I have a TV room with a queen-sized fold…