Because of the nature of the work, extras don't have a regular employer, though they may work for some of the same filmmakers and TV productions. Extras are needed not only for movie and TV shows, but also for commercials, music videos, and interactive games.
For regular work as a film or TV extra, you'll have more success living where the bulk of films and TV shows are filmed, around Los Angeles or New York. Though some productions may place ads for extras in local newspapers or on the Internet, you will benefit the most by having an agent. There are agents who work exclusively with extras, as opposed to principal actors' agents. Extras agents typically charge a registration fee (usually less than $30) and a 5 to 10 percent commission. When selecting an agent, watch out for scams; carefully read all contracts and be wary of agents with large registration fees or those who claim to "guarantee" work. For information about reputable agents, you can check with your local film commission or local division of SAG-AFTRA.
By talking to other extras and crew members, beginning performers can learn more about the film industry and may make some valuable connections. Unfortunately, there are no guarantees for success in the film industry; even years of experience may eventually lead nowhere. However, extras may be able to use connections they've made through union membership and working on productions to get more major auditions for supporting or major roles on films and TV shows.
Use social media such as LinkedIn, Facebook, and Twitter to stay up-to-date to learn about open calls for extras.
As a student, gain experience by acting in school or local theatrical productions.
Look for jobs and/or market your services at Mandy.com. Other useful sites include Infolist.com and EntertainmentCareers.net.
Read Backstage (http://www.backstage.com) for advice on becoming an actor, as well as job listings.
Participate in acting workshops, seminars, and other training opportunities.