Yoga teachers live their yoga practices and attempt to teach that way of life. These teachers apply the ethical and spiritual principles of yoga to their own lives and their instruction.
For example, the Yoga Sutras describe yoga as having eight limbs, so a classical yoga teacher would include these limbs as part of their instruction. In addition to teaching asanas and pranayama (breathing exercises), the instructor would also include yamas and niyamas (virtues and rules of living), pratyahara (control of the senses), dharana (inner awareness), dhyana (devotion) and samadhi (union with the Divine).
In it’s best manifestation, a yoga teacher is someone who stands witness with you and steadily points the way to your own empowerment.