Stand with your spine upright, and expand your chest for breath support. Keep your shoulders relaxed.
Identify the difference between tension (unhealthy) and relaxation (healthy) by stretching your arms up over your head and lengthening the stretch all the way to your fingertips. Drop your hands so that they hang loosely. The resultant energized feeling in your hands is relaxation; the tight feeling of the muscles in your arms supporting the hands is tension. Focus on releasing tension from the abdominal area and the articulators: the jaw, tongue, palate and lips.
Develop healthy breathing habits. Stand with an upright posture, and place your hands on your abdominal wall, feeling it expand as you allow breath in and deflate as you release breath. Picture your diaphragm moving down to allow oxygen to enter the lungs as you inhale and rushing upward as you exhale. Familiarize yourself with this breathing technique visually and physically.
Practice releasing voice "on the breath" with lip trills (blowing air through loose lips so they flutter) to avoid tension on your vocal cords. Use the lip trill exercise with sheet music, scales or lyrics to warm-up the voice and relax the lips.
Open your throat, and release a scream on your breath with a completely relaxed jaw. Yawn several times before screaming to familiarize yourself with the correct positioning of the jaw. Enlist a vocal coach to provide feedback.