Depending on what your interest in theater is, I always recommend working on plays. It's a great way to be introduced to the field, and also a great way to be seen by agents and representation. I'm also a great advocate for studying acting at a drama school or a college.
“The creative individual has the capacity to free himself from the web of social pressures in which the rest of us are caught. He is capable of questioning the assumptions that the rest of us accept.”