“ Drop in anytime” and “come see me soon” are idioms often used in social settings but seldom meant to be taken literally. It is wise to telephone before visiting someone at home. If you receive a written invitation to an event that says “RSVP”, you should respond to let the person who sent the invitation know whether or not you plan to attend.
Never accept an invitation unless you really plan to go. You may refuse by saying, “Thank you for inviting me, but I will not be able to come.” If, after accepting, you are unable to attend, be sure to tell those expecting you as far in advance as possible that you will not be there.
Although it is not necessarily expected that you give a gift to your host, it is considered polite to do so, especially if you have been invited for a meal. Flowers, chocolate, or a small gift are all appropriate. A thank-you note or telephone call after the visit is also considered polite and is an appropriate means to express your appreciation for the invitation.