In the background. The salesperson knows the buyer's requirements and can better emphasize the features of your home when you don't tag along. This is their job. If you're not leaving while we are showing your home please disappear. If we need you we will certainly find you.
Silence is golden.
Be courteous but don't force conversation with the potential buyer. They want to inspect your home, not pay a social call. When they talk to you, their not looking at the home. Trying to dispose of furniture and furnishings to the potential buyer before they buy, often loses a sale. We usually avoid this completely until after closing when there is still plenty of time.