Depending on where you live, you might want to see if there’s a theater conservatory program in your area that you can participate in during high school as an extracurricular to build up experience and performance skills. Also, if you’re taking dance or voice classes, continue with those. You also need to keep your academics up, and choose challenging classes, because the average income for an actor from acting is $5000 a year, and you may find that you need to work in another theatrical field in order to support yourself.
Here is a link you might find helpful. Becoming an actor is a lot of hard work, with a lot of talented competition.