Presanctified Liturgy

The Presanctified Liturgy is an ancient and beautiful service held only during the Great Fast preceding the feast of the Resurrection. As the joy of the Eucharistic Liturgy is inappropriate during the weekdays of the Fast, but the faithful are in even greater need of being strengthened by Holy Communion, the Eucharist consecrated on Sunday is kept and distributed during a special vesperal liturgy on Wednesdays and Fridays (or other days during the week) throughout Lent. The service is deeply penitential, but filled with the assurance of Christ’s love in giving Himself to us in Communion.

Here is a good pamphlet from St. Vladimir Orthodox Church for when to prostrate during the Presanctified Liturgy
http://www.stvladimiraami.org/pamphlets/presanctifiedliturgytips.pdf