In the Catholic liturgical year, December is the month of the Immaculate Conception. It is not, as I thought for so many years, the Immaculate Conception of Jesus, but the Immaculate Conception of his mother, Mary. It represents God’s saving grace, in recognition of Mary’s complete submission to his will.
My favorite prayer to add to this month:
To the Virgin Immaculate
O Virgin Immaculate, Mother of God and my Mother, from thy sublime height turn upon me thine eyes of pity. Filled with confidence in thy goodness and knowing full well thy power, I beseech thee to extend to me thine assistance in the journey of life, which is so full of danger for my soul. And in order that I may never be the slave of the devil through sin, but may ever live with my heart humble and pure, I entrust myself wholly to thee. I consecrate my heart to thee for ever, my only desire being to love thy divine Son Jesus. Mary, none of thy devout servants has ever perished; may I too be saved. Amen.
Also, in the habit of praying without ceasing, you could add this to your day:
Aspiration to Mary
O Mary, conceived without sin, pray for us who have recourse to thee.
More prayers for this month can be found at About.com’s Catholicism section.