It's time to start work on the "O antiphons" so that you can be familiar with them and sing them naturally and comfortably when the time comes.
Here is the Catholic Encyclopedia on their history and meaning.
The seven antiphons to the Magnificat in the ferial Office of the seven days preceeding the vigil of Christmas; so called because all begin with the interjection "O". Their opening words are: (1) "O Sapientia", (2) "O Adonai", (3) "O Radix Jesse", (4) "O Clavis David", (5) "O Oriens", (6) "O Rex Gentium", (7) "O Emmanuel". Addressed to Christ under one or other of His Scriptural titles, they conclude with a distinct petition to the coming Lord (e. g.: "O Wisdom … come and teach us the way of prudence"; "O Adonai … come and redeem us by thy outstretched arm"; "O Key of David … come and lead from prison the captive sitting in darkness and in the shadow of death" etc.). Couched in a poetic and Scriptural phraseology they constitute a notable feature of the Advent Offices. These seven antiphons are found in the Roman Breviary...
