As a Guest you may have the run of the house, but do not assume that you do. Always ask permission to visit an upstairs bathroom, for example, if the downstairs bathrooms are occupied.
If you are given permission to use the upstairs facility by the hostess, but she does not indicate that you can have a tour of her home, just use the facility and go back downstairs as quickly as possible. It is rude to assume you can tour the home unless given permission to do so.
During the party, stay out of the kitchen. You will be in the way! Besides you were not invited to help cook or oversee the meal preparation.
Never touch anything that belongs to your hosts. If the host has a selection of fine cigars, do not assume that as his guest he wants you to take your pick. If your hostess has fine perfume on her dressing table, do not assume that she wants to share it with you. Do not look in the closets, drawers, or medicine cabinets, etc.