The best way to learn is experience and education. Take a massage therapy program as it usually includes instruction on how to give a salt glow massage. A licensed massage therapist can take continuing education courses on the subject. Practice on a classmate, friend or a family member. Take notes on the process and what is needed for the massage.
Buy or rent a video that provides information and techniques on how to give a salt glow massage. This is also a good way to better this skill if already being taught in the classroom. Study books on this subject.
Work at a spa. Learn the techniques of this type of massage from someone who delivers them on a frequent basis. Learn from an expert.