To determine the most auspicious date for something, recite the Orphic Hymn to Hekate:
Lovely Hekate of the roads and crossroads I invoke;
in heaven, on earth, and in the sea, saffron-cloaked,
tomb spirit, reveling with the souls of the dead,
daughter of Perses, haunting deserted places,
delighting in deer, nocturnal, dog-loving, monstrous queen,
devouring wild beasts, ungirt, of repelling countenance.
You, herder of bulls, queen and mistress of the whole world,
Leader, nymph, mountain-roaming nurturer of youth, maiden,
I beseech you to come to these holy rites,
ever with joyous heart and ever favoring the oxherd.
And then spin the Key on the Wheel. The Wheel is a circle with thirty spaces marked out along its rim and thirteen towards the center. Each of the thirty represent a day of the month and each of the thirteen represent a month of the year. Place them on the wheel in a random order and leave empty spaces so that Hekate may decline to answer if the undertaking is not at all auspicious. The Key is a key.