Start simple. While many girls dream of seeing their faces on television and movie screens, the truth is that most young actors and actresses get their starts in local theater groups and television commercials. Check into the theater group in your town and school, and get involved. Even if you only score small roles in the beginning, persistence, enthusiasm and practice will help you climb into larger roles later. This will also expose you to a variety of genres, from the classics, to more modern productions, giving you a wide range of experience that will come in handy later on.
Sign up for acting classes. Professional training is a surefire way to make sure you learn all the ins and outs of acting. Line delivery, facial expression, emotional connotation and even how and where to audition for some early roles. Don't just focus on the acting aspect while you're learning. Learn about the ins and outs of the business, the people who work behind the scenes, and don't be afraid to volunteer for behind-the-scenes positions yourself if they become available to you. Working on set will help expose you to people who might be able to help you get jobs later on down the road.
Put together a press package with head shot photos, and a portfolio of your resume and experience. Send this out to agencies that specialize in representing teen talent. Garnering quality representation will help you get acting jobs and introduce you to other people who want to work with you in the future.
Consider auditioning for local commercials. Thousands of actors and actresses got their start in commercials, and if you can score some commercial work, it could help you get your foot in the door when you're ready to start auditioning for larger roles. Building a strong resume and experience are essential, and this will also provide early networking experience. The people you meet in commercials may even be able to recommend you to other producers looking for talent.
Involve your parents in every aspect of your career. They will always have your best interest in mind, and while you may not always agree on roles and job opportunities, they may be able to protect you from scams and bad opportunities.
Stay focused. It is important to strive toward what you want with a vengeance, but don't let it interfere with the other areas of your life, like school and family. Getting a good education is necessary to your career. Even high-power actresses like the Olsen twins went on after high school to get college educations, because you never know what awaits you in the future.