You shall observe Lord Caitanya's birth day as follows:
1. The picture of Lord Caitanya with His party should be nicely decorated with flowers and garlands and Sankirtana should be performed regularly from Morning to evening. Just after seeing the Full Moon on the sky the days fast should be broken. I mean the devotees should observe fasting the whole day. In the evening the devotees should take food as in the Ekadasi days.
2. The next day you can celebrate feasting on account of Lord Caitanya's appearance and read about His life as given shortly in my Srimad-Bhagavatam and you can read also from the teachings of Lord Caitanya part of which is going to be published in the present issue of Back to Godhead.
Letter to: Brahmananda — San Francisco 14 March, 1967
Lord Caitanya's Birthdate is on the Phalguna Purnima between 15 of Feb. and 15th of March. The full moon day is Lord Caitanya's Birthday. I think you can send for Rayarama's calendar which he has published. The exact day is 14th March, Thursday, 1968. The procedure is that you should fast from morning to evening (about 7:00) after that there should be offering to Lord Caitanya and prasadam should be accepted just like on Ekadasi day, and next day, Friday, full love feasting may be provided to as many devotees as you can.
Letter to: Janardana — Los Angeles 21 January, 1968
So far the Advent Day of Lord Caitanya is concerned, I have written a full suggestion to Montreal, in which the main points are that we should all observe strict fasting up till moonrise, and at that time, an offering is made to Lord Caitanya of Ekadasi foods, fruits, peanuts, milk, and so forth. Then, on the next day, Friday the 15th, a full-scale feast is held to celebrate His Advent Day. On the 14th, chanting, reading of Srila Bhaktivinode's book, Life and Precepts and Caitanya Caritamrta, Introduction to Bhagavatam, may be held all the day in the Temple.
Letter to: Balai — San Francisco 12 March, 1968
Lord Caitanya's Appearance day falls on March 22, that is on a Sunday. The devotees should fast until evening, when there is a ceremony and offering of a small amount of Ekadasi preparations. The next day, the devotees should celebrate amongst themselves with a small scale feast.
Letter to: Krsna dasa — Los Angeles 18 February, 1970
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.
Letter to: Mahapurusa — Los Angeles 7 March, 1968