On prostrations, and what kind are to be done during the Liturgy.
http://www.stjohndc.org/russian/english.htm
According to the rules of the Holy Orthodox Church, full prostrations (head to the ground) - symbolizing extreme humility before God - are not done on Sundays, for on those days we celebrate a little Pascha. On the day of His Glorious Resurrection from the dead, Christ the Savior reconciled us to God.
Full prostrations are, however, called for during Liturgies served on weekdays. The first full prostration in the Liturgy is done after the Creed, as the priest says "Let us give thanks unto the Lord!" and the choir responds by singing "It is meet and right to worship the Father, Son, and Holy Spirit…" At that point the priest reads a prayer in which he thanks the Lord for bringing us from non-being into being, for once again restoring those who had fallen away from Him. He thanks the Lord for all of His blessings, both those we know of and those unknown to us, and for the peaceful sacrifice ("a mercy of peace"), that we are about to offer. Thanks to this prayer of thanksgiving, the entire impending church service is known as the "Eucharist," from the Greek word meaning "thanksgiving." All of the faithful perform the first full prostration at this point as a sign of their thanks to God for their entire lives.
Everyone makes a second full prostration at the singing of "To Thee we sing…," i.e.. during the Mystery of the changing of the Holy Gifts, at the priest's words "changing them by Thy Holy Spirit. Amen. Amen. Amen!"
Christ Himself is present in the Holy Gifts. Everyone makes a third full prostration to the Mother of God at the words "Especially for our Most holy, Most pure, Most-blessed, Most-blessed Lady Theotokos and Ever virgin Mary." At this time, the Choir sings "It is truly meet to bless thee, the Theotokos…" We revere the Mother of God as "more honorable than the Cherubim and beyond compare more glorious than the Seraphim." By her was the Incarnation of God accomplished. She gave birth to God our Savior.
The ustav calls for a fourth full prostration at the singing of the "Our Father," the Lord's Prayer, for us is of absolutely unique importance. It is the greatest of prayers, for it was given to us by the Lord Himself (see Matthew 6: 9-13). As we pronounce the words "give us this day our daily bread," let us think not only of ordinary bread, but about the eucharistic Bread of which many soon are to partake. Let us pray that the Lord might give us "this day" His divine Bread, unto the healing of soul and body.
We make the fifth full prostration when the Holy Gifts are brought out for Communion of the laity, as the priest or deacon says "With fear of God, with faith and love draw nigh!" According to the Orthodox Faith, in the Mystery of the Eucharist bread and wine changes into the Body and Blood of Christ. We bow down before the Holy Gifts as before Christ Himself, for He is mystically present in them.
The sixth full prostration is done at the end of the Liturgy, after the singing of "We have seen the True Light…" At this point, the priest secretly prays: "Be Thou exalted above the heavens, O God, and Thy glory above all the earth!" In the Liturgy, this final appearance of the Holy Gifts to the people, and their subsequent transfer deep into the Altar, to the Table of Prothesis, depicts the Ascension of Jesus Christ into Heaven. The Gospel states that while Christ was ascending, the Apostles bowed down before Him (Luke 24: 52); likewise, at the final appearance of the Holy Gifts we make a full prostration. Those who have communed do not make this last prostration, for they not only observe and contemplate on Christ as the other faithful do, but they also have Him within themselves!