This is the best introduction to Vedanta and to Sankara's philosophy. The Upadesaasahasri, or A Thousand Teachings consists of a metrical part and a prose part. In the metrical part, Sankara discusses the basic philosophical problems of non-dualism, at the same time refuting the teachings of other philosophical schools. In the prose part, he explains how to teach the way to self realization--to enlightenment.
Sankara and the great Abhinavagupta are generally regarded as the two greatest thinkers in the long history of Indian philosophy. Sankara represented Advaita Vedanta, a non-dualistic view of ultimate reality. Most of his works are commentaries on classics of Indian thought. A Thousand Teachings is the only non-commentarial work that can be attributed to him; the other independent writings ascribed to him are probably spurious.