There are lines and areas on the radar scope that are pre-coordinated to handoff to the next controller. There is a little bit more to it. I would suggest you take a trip to your local tower, TRACON and ARTCC of you can. They allow tours for student and current pilots. In fact, they encourage it. The more you know about both sides of the system, the better understanding of the system you have and therefore, the safer pilot you are.
Reference the attached pictures.
In SOCAL, it's usually pretty difficult to anticipate frequency changes due to the complexity of the airspace. Sector staffing changes daily based on how many controllers are available to work, weather and traffic volume. Often times, when one controller works two or more sectors, a frequency change will not always occur if it results in you talking to the same controller, assuming one frequency has the range to cover the controller's entire jurisdiction.
Outside of SOCAL, it's not hard to determine whereabouts you'll receive a frequency change. Most TRACONs are not as complex as SOCAL, and the frequencies usually remain the same day-to-day. Once you reach a pre-coordinated position along a route of flight, a handoff is initiated and accepted by the next controller, where you then receive the transfer of communications. If you fly in the same area on a regular basis, you begin to recognize where those fixes are. This assumes you're flying at the same altitude each time.
