Unless you're talking to a visitor who prefers to sit, stand. Don't sit between visitors. When you are not on duty, don't hang around your own exhibit. Visit other displays. Or get off your feet.
Many shows have exhibitor lounge area or convenient coffee shops or bars.
You need the change. Besides, an off-duty presence makes the booth seem crowded and discourages visitors. The finest exhibit booth with the most exciting design comes to life only when effectively staffed. Identify yourself and position by wearing a name tag. Keep the display and surrounding area clean.