Your DJ should be polite and courteous to you, your guests and other vendors. They should also be able to work seamlessly with with all other vendors, i.e. planner, caterers, photography, etc. Your DJ should be professionally dressed and dressed appropriately for the event. The equipment area should be clean and well-maintained. Your DJ should arrive early enough to have all equipment set up outside the presence of guests.
Your DJ should be flexible in scheduling meetings and phone calls. Your DJ should also be adaptable to changes, even last-minute changes, in the timeline, schedule, etc.