Make sure the course is properly measured. Check the distance and split times. The event should have frequent mile or kilometer markers, or both, and clocks or split timers. Find out about water. The race should include water at the start, at almost every mile or kilometer, and at the finish.
Sports drinks are a benefit, too.
Survey the location. If either is more than 30 minutes away, make sure bathrooms are available - perhaps on a bus to the start. Go for an Expo. It's preferable that the race registration include one, with exhibits, demonstrations and services for runners. It is an important part of the ambience.