Book your ticket at least a week in advance, if possible. Some bus companies raise their fares for those who book at the last minute.
If you are traveling to Las Vegas from a location in Southern California, Nevada or Arizona, consider riding one of the more local bus lines, such as Tufesa or LuxBus America. If you are traveling from further away, book through a wider-ranging bus company such as Greyhound.
If you are traveling with a large group of people, look into chartering a bus to Las Vegas. Ask companies such as Greyhound and Celebrity Coaches of America about group discounts and theme buses (such as party buses).
