Move to a city that regularly films movies and television. Large metropolitan areas like New York City, Los Angeles and Toronto, Canada, are some of the best spots.
Contact an agency that specializes in providing extras to production companies. To become a movie extra, you must have this go-between to ensure you're treated and paid fairly.
Make yourself available for contact by the talent agency. Often jobs simply go to the people who answer the phone first when they are called.
Have realistic expectations about the amount of money you're going to make as a movie extra. The amount is only supplementary and the work can be sporadic.
Bring along a book or other means of entertainment when you're called for a project. After you become a movie extra you'll find that you have a great deal of time to kill as camera angles are set up.
Remain professional when you're on the set. Resist the temptation to become star struck and ask celebrities to pose for a picture when they might be otherwise occupied.