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 Second Sunday of Advent from the Traditional Latin Mass; you could also use the Opening Prayer for the Second Sunday of Advent from the current missal.
Last week, we asked Christ to come to our aid; this week, we ask Him to move us to action, so that we can prepare ourselves for His coming at Christmas.
Advent Wreath Prayer for the Second Week of Advent
Stir up our hearts, O Lord, to prepare the ways of Thine only-begotten Son, that through His coming we may be worthy to serve Thee with purified minds. Who livest and reignest, with God the Father, in the unity of the Holy Ghost, God, world without end. Amen.