You should always consider the following questions when booking a gig:
Music: What style/genre are you expected to play? Are there any special requests in the repertoire?
Time: What are the event start and end times? Will there be a soundcheck? Will the requestor allow the performers a small break per hour (10-15 minutes)?
Location: Where is the gig located? Are the provided travel directions clear? Will there be parking available on site?
Space: Is there a designated space for the performers? If performing outdoors, is there a plan for inclement weather? Are power outlets nearby? Does the space have access to an elevator?
Equipment: If a piano is provided, when was it last tuned? Are chairs and stands available? Will you need to provide your own amps and cordage?
Attire: Will you be required to wear specific clothing for the gig? Is there an event theme?
Food: If dinner is served at the event, will musicians be provided with food?
Contact: Is there a specific point-person to communicate with for the event outside of the event requestor? Can you exchange cell phone numbers and email addresses?
Payment: What is the fee for the gig? Will you be paid via check or electronic deposit? Is parking or transportation included in the fee, or will it be added as an extra charge?