Code of Canon Law:
Can. 1249 All Christ's faithful are obliged by divine law, each in his or her own way, to do penance. However, so that all may be joined together in a certain common practice of penance, days of penance are prescribed. On these days the faithful are in a special manner to devote themselves to prayer, to engage in works of piety and charity, and to deny themselves, by fulfilling their obligations more faithfully and especially by observing the fast and abstinence which the following canons prescribe.
Can. 1250 The days and times of penance for the universal Church are each Friday of the whole year and the season of Lent.
Can. 1251 Abstinence from meat, or from some other food as determined by the Episcopal Conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday.
Can. 1252 The law of abstinence binds those who have completed their fourteenth year. The law of fasting binds those who have attained their majority, until the beginning of their sixtieth year. Pastors of souls and parents are to ensure that even those who by reason of their age are not bound by the law of fasting and abstinence, are taught the true meaning of penance.
Can. 1253 The Episcopal Conference can determine more particular ways in which fasting and abstinence are to be observed. In place of abstinence or fasting it can substitute, in whole or in part, other forms of penance, especially works of charity and exercises of piety.
Prayer to the Glorious Cross:
I adore You, O glorious Cross, which was adorned with the Heart and Body of my Savior Jesus Christ, stained and covered with blood. I adore You, O Holy Cross, out of love for Him, Jesus, who is my Savior and my God.
(Pope Pius IX declared that reciting this prayer five times on Friday will free five souls from Purgatory and 33 souls by reciting it on Good Friday. This prayer should be recited before a crucifix with a contrite heart and praying a few minutes for the Pope).
Prayer to Jesus Christ Crucified:
My good and dear Jesus, I kneel before you asking you most earnestly to engrave upon my heart a deep and lively faith, hope, and charity, with true repentance for my sins, and a firm resolve to make amends. As I reflect upon your five wounds, and dwell upon them with deep compassion and grief, I recall the words the prophet David spoke long ago concerning yourself: they have pierced my hands and my feet, they have numbered all my bones!