Tradition and History
Gaura Purnima is the birthday of Lord Caitanya (1486-1534) who started the congregational chanting of the names of God. He specifically recommended the chanting of the maha-mantra: Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. His followers consider Him to be Krishna, or God Himself.
On this day everyone fasts, visits the temple to see the Deities (images) of the Lord, hears about Lord Chaitanya's activities and chants Hare Krishna accompanied by drums (mridangas) and hand cymbals (kartalas). At moonrise a very big vegetarian feast is served and everyone returns home very happy.

How to observe the Festival
At the meeting everyone should try to speak something on Caitanya Mahaprabhu's life, teachings, and philosophy. You can take quotations from the above mentioned books, and have discussions.
Fasting should be continued up to evening, then you may have food like on Ekadasi, fruits, milk, etc. On the next day you may observe festival. Janardana consulted me and said he thinks Sunday feasting would be best, so you may do that if you like. Or you may do both days, as you feel best.
Letter to: Mahapurusa -- Los Angeles 7 March, 1968

Fasting until moonrise