Stand backwards against a wall and place your heels about 2 inches from the wall.
Push the small of your back against the wall.
Keep your head level.
Tuck your buttocks under. Your chest should now come up, with your shoulders moving back. This is the proper body alignment for singing.
Combine the posture exercise with breathing exercises.
Stand erect.
Place one hand on your abdomen.
Open your mouth and exhale with a soft "ha!" sound.
Keep your chest up and pull your lower abdomen in and gently follow your breath out.