Talk to your adult son or daughter about how long they want to stay at home for and why. Express your own views and reach a compromise. Communication is the key to improving relations with anyone. Remember that communication is a two way thing and involves you listening as well as your son or daughter.
To reduce friction, write out a contract outlining rules for food, expenses, chores and sharing facilities (such as the cooker and washing machine). Wage earners living at home should pay their own way as well as sharing household tasks. It is not always about the money, it will also prepare them for independence.
Install a contributions box next to the telephone. If you're desperate to stop calls, buy a phone lock
Coordinate social plans by encouraging everyone to use a family diary or bulletin board. (A parents' night out at the theatre might be a good time for an adult son or daughter to have friends around, for example.) Set aside one evening a week or month for the whole family to have dinner together or perhaps go out for a drink.
Invest in large stackable, plastic containers (or vegetable racks) to store excess books and baggage until your child moves out. These containers are available from most hardware stores.