Here is a beautiful prayer before Holy Communion written by St. Thomas Aquinas, Doctor of the Church whose feast is celebrated on January 28th. One can recite this prayer before the beginning of Mass or before receiving the Eucharist. Let us approach the most Blessed Sacrament with humility and reverence, without any stain of mortal sin.
Almighty and eternal God, behold, I come to the sacrament of Thine only-begotten Son, Our Lord Jesus Christ. I approach as one who is sick to the physician of life, as one unclean to the fountain of mercy, as one blind to the light of eternal brightness, as one poor and needy to the Lord of heaven and earth.
Therefore I beseech Thee, of Thine infinite goodness, to heal my sickness, to wash away my filth, to enlighten my blindness, to enrich my poverty, and to clothe my nakedness, that I may receive the Bread of Angels, the King of Kings, and the Lord of Lords with such reverence and humility, with such contrition and devotion, with such purity and faith, with such purpose and intention, as may be conduce to the salvation of my soul. Grant, I beseech Thee, that I may receive not only the sacrament of the Body and Blood of our Lord, but also the fruit and virtue of this sacrament.
O most indulgent God, grant me so to receive the Body of your thine-begotten Son, Our Lord Jesus Christ, which he took of the Virgin Mary, that I may be found worthy to be incorporated with his Mystical Body and numbered among His members. O most loving Father, grant that I may contemplate forever, face to face, Thy beloved Son, whom now on my pilgrimage I am about to receive under the sacramental veils; Who lives and reigns with Thee in the unity of the Holy Spirit, God, world without end. Amen.
– Saint Thomas Aquinas