Today we celebrate Buddha’s descent from Tushita Heaven. This is one of the four major Buddhist holy days (the day of miracles, the day the Buddha was enlightened, the day the Buddha first taught the four noble truths, and the day he descended from the god realm of Tushita to earth).
Gyumed Khensur Rinpoche Losang Jampa suggests that we chant the Praises to Shakyamuni Buddha prayer and any other prayers related to Shakyamuni Buddha.
Buddha Shakyamuni ascended to The Heaven of Thirty-Three in order to give teachings to benefit the gods in the desire realms and to repay the kindness of his mother by liberating her from Samsara. This is considered to be one of the great deeds of the Buddha among eight great deeds. On Lha-Bab Duchen, the effects of positive or negative actions are multiplied ten million times. It is part of Tibetan Buddhist tradition to engage in virtuous activities and prayer on this day.
(source: http://www.gyutocenter.org/component/content/article/112-special-annoucment.html)
