Traditionally, the prayers used for the Advent wreath for each week of Advent are the collects, or short prayers at the beginning of Mass, for the Sunday of Advent that begins that week. The text given here is of the collect for the First Sunday of Advent from the Traditional Latin Mass; you could also use the Opening Prayer for the First Sunday of Advent from the current missal.
We begin this first week of Advent by asking Christ to come, to set us free from our sins and from the punishment that we deserve. He is our salvation.
Advent Wreath Prayer for the First Week of Advent
Bestir, O Lord, Thy might, we pray thee and come; that, defended by Thee, we may deserve rescue from approaching dangers brought on by our sins, and being set free by Thee, obtain our salvation. Who livest and reignest, with God the Father, in the unity of the Holy Ghost, God, world without end. Amen.