Penance is define as "voluntary self-punishment inflicted as an outward expression of repentance for having done wrong". The penitential season in the Church is called Lent which begins on Ash Wednesday and continues till Easter. During this season Christians are obliged to fast, and on Fridays, abstain from meat. Those not obliged to fast, can do other forms of penance.
Ash Wednesday the minister places ashes on the foreheads of Catholics with the words, "Remember you are dust and into dust you shall return". In other words, stop being involved so much with worldly cares because at death you will leave everything behind and meet God who will judge you. Pope Frances says the following: "during the forty days of Lent, as Christians we are called to follow in the footsteps of Jesus and address the spiritual battle against evil with the power of the Word of God. For this you have to become familiar with the Bible, read it often, meditate on it, assimilate it. ... Don't forget what would happen if we treat the Bible as we treat our cellphone, always with us!" Christianity on News 360)
Indeed, you can download the compete Bible on your cellphone so it will be readily available to you.
If you go to Google Playstore you can download it for free and the font size can be adjusted to the size you prefer. You may not be naturally inclined to read the Bible every day, but this penance will benefit of your soul.
Why do penance?
1. To show God that you love him above all earthly things.
2. To make make up the for the punishment you sins deserve.
3. To gain more control over your passions.
Another penitential prayer are the Stations of the Cross. Contemplation on the suffering of Christ is the traditional way of prayer during Lent. Here we reflect on the love of God and the sufferings sin brings into our live.
The third way of of sacrificing is to do one or more of the works of mercy (e.g. feed the hungry, visit the sick, etc.)