Saint Michael is invoked in the Litany of the Saints. This ancient prayer is used both communally and privately. Part of the litany is listed below.
Lord, have mercy on us. Christ, have mercy on us. Lord, have mercy on us. Christ, hear us. Christ, graciously hear us.
God, the Father of heaven, have mercy on us.
God the Son, Redeemer of the world,
God of the Holy Ghost,
Holy Trinity, one God, have mercy on us.
Holy Mary, pray for us.
Holy Mother of God,
Holy Virgin of virgins,
All ye holy angels and archangels,
All ye holy orders of blessed spirits,
Saint John the Baptist,
All ye holy patriarchs and prophets,
[the rest of the Litany is here]
The invocation to those in the heavens to pray is a recognition that just as someone would go to a fellow church member for prayer on earth, so it is possible to ask for those who are already in the heavens for prayer.