Practice your acting craft. The best actors have an acting coach who is well versed in the theater circuit. Theater acting is about skill and craft whereas film acting is more about image.
Compile a resume. Most theater actors have a resume with vital statistics such as age, height, weight and vocal characteristics if you have singing talent. Of course, list your productions and acting roles.
Research theater houses or production companies in your area or the area where you want to act. Make sure you find out where they hold auditions so you can appear with your resume in hand.
Prepare for your auditions. It's best to plan to attend numerous auditions for roles you would want to play. Rejection is inevitable with acting, so it shouldn't discourage you.
Try to read for as many roles as possible, since it will increase the likelihood of getting a part. Theater actors often start as extras or in supporting roles before receiving leads.