Let your breath relax with the pace of the chant, perhaps let your voice hum with the tones, then move into doing the chant. The syllables are quite powerful. Let thoughts dissolve and be with your breath. OM Namah Shivaya is called the great redeeming mantra, leads the soul home, and awakens the inner guru. Shiva is consciousness and the true guru, your own Self. "Guru", by the way, means to come from light from darkness.