This is a great article of the proper practice of when to prostrate during the Liturgy. The link is listed at the end of the article. Thank you Fr. John Whiteford! Here is the text:
We do not make prostrations at all on Sundays, with the exception being the veneration of the Cross on the third Sunday of Lent, or when the feasts of the Exaltation of the Holy Cross or the Procession of the Cross fall on a Sunday.
We also do not make prostrations on feasts of the Lord (except for the veneration of Cross), regardless of what day they fall on.
We do make them on great feasts of the Theotokos, unless they fall on a Sunday.
During the Church Year, we stop making prostrations after the Presanctified Liturgy on Holy Wednesday, with the only exception being the veneration of the Epitaphios (Plashchanitsa) at Holy Friday Vespers, and Holy Saturday Matins. Even though the Epitaphios remains out until just before Paschal Matins (in Russian practice), prostrations are not supposed to be done when venerating it after the Matins of Holy Saturday (which is actually served Friday evening). We do not make prostrations again until the Kneeling Vespers of Pentecost.
Keeping the above in mind, at Liturgies that do not fall on Sundays or Feasts of the Lord, there are five points at which prostrations should be made:
1. At the Anaphora, the priest or bishop says “Let us give thanks unto the Lord.”
2. At the end of the hymn: “We praise Thee, we bless Thee, we give thanks unto Thee, O Lord; and we pray unto Thee, O our God.” For those in the Altar who are able to hear it, this should be done when the priest or bishop says “Changing them by Thy Holy Spirit.” That prayer is traditionally said in a low voice, while the hymn is being sung, and so the people usually do not hear it said.
3. At the end of the hymn to the Theotokos at the Anaphora: “It is truly meet,” or its substitute (Zadostoinik).
4. When the chalice is brought out by the deacon or priest, and he says”With the fear of God and with faith, draw nigh.” The clergy do not prostrate at this time, because they do this earlier in the Altar, before they commune.
5. When the chalice is shown to the people for the last time, and the priest or bishop says “Always, now and ever, and unto the ages of ages.” The common practices, however, is that those who have received communion do not make a prostration at this point, and so the clergy likewise do not make a prostration.
It is also a common practice in some local traditions to make a prostration when we sing the “Our Father.” However, according to Archbishop Peter, St. John of Shanghai taught that this was incorrect, because, as we say just before we sing this prayer at the Liturgy, we are asking that God would enable us “with boldness and without condemnation to dare to call upon [him] the heavenly God as Father…” And a son does not prostrate himself before his father, when he has such boldness and is not under condemnation.