Earn an associate or bachelor's degree. While not a requirement, a college education provides a solid foundation for becoming a casting assistant, especially if you major in theatre or film.
Find an internship with a casting agent or a casting firm. Websites such as Dream Careers, Extras Casting Agency and Central Casting all accept applications for unpaid internships. These are highly competitive positions—applicants with master's degrees routinely contend for the few available spots. But the experience and contacts you make working on the "inside" are invaluable.
Apply for a position as an assistant to a talent agent in New York or Los Angeles, the two busiest cities for acting in the country. Working on a talent agent's desk gives you first-hand experience with the ins and outs of how producers solicit actors and make offers, and how agents close deals. It also provides you with access to new, up-and-coming actors you have to know as a casting assistant. Another important benefit of this position is the opportunity to read scripts so you can develop the skill of matching actors to specific roles. Most talent agent assistants begin as mail room workers in major agencies and work up to the assistant level.
Obtain production assistant, or PA, jobs on movie sets to learn the behind-the-scenes requirements for feature films and TV shows. As a PA, you perform a number of physical jobs, including carrying equipment, calling actors from their trailers and watching how a director shapes performances. This is crucial experience that can help sharpen your talent recognition skills, which is necessary to be an effective casting assistant.
Apply to casting assistant jobs. Use online resources such as the Crew List Job Board, Media Match and Crew Net. These sites allow you to register for free so you can post your resume and apply for jobs online. With a few exceptions, many casting assistant positions are in New York or Los Angeles.