Approach acting as a job. If you are serious about getting started in movies, it is important to approach the concept as an actual career. Invest a lot of time in preparation for a career in acting, such as subscribing to trade papers, reading acting books, taking acting classes and networking with any people you meet that are somehow involved in the movie industry. Be proactive and approach acting from all different sides. Don't simply wait around for someone to "discover" you and cast you in a movie because that likely isn't going to happen.
One way in which to try to get your foot in the door is by being an extra on a movie set. Another common term for an extra is a "background actor." Extras generally do not speak any lines in movies. Look in your local paper to find out if any movie productions soon will be in your area. Working as an extra can be beneficial for providing you with an upfront look at how a film set operates.
Act in a student film. Chances are, there is a college or university in your area. If the school offers a film program, it's likely that they produce student films. Contact the film department and offer your services as an actor. Even though you probably will not receive any payment, you will receive invaluable experience and also will be able to use your performance in the film as part of an acting reel.
Seek out independent movies. Indie films can be useful for getting experience and getting your foot in the door. Seek out open casting calls for low-budget movies in your area. Scan through your local paper or through trade publications to find listings for opportunities. Similar to student films, you likely will not get paid, but you will get some hands-on acting experience that can help you later.
Look for an agent. To get movie roles, it is necessary to hire an agent who will be able to help you secure jobs. Construct an acting reel (using your roles in independent films, student films, etc.) that your agent will be able to use to shop around to get you parts in movies. Hiring an agent to do these things can be much more effective than doing them yourself. After all, agents network a lot and have significantly more industry contacts.