When considering a banquet hall, check to see what services are included in the rental fee. In addition to providing the food and all the equipment, they might also provide party hats and favors, valet parking, and even coat-room and restroom attendants.
After you book your banquet hall, have the management send or fax you a copy of the booking agreement. You should keep this in a safe place, so that you're protected if something goes wrong on the management end of the deal, or if there's a dispute.