Lent: Prayer, Fasting, Almsgiving
Lent (the word "Lent" comes from the Old English lencten, meaning "Springtime") lasts from Ash Wednesday to the Vespers of Holy Saturday - forty days, nevermind the six Sundays which don't count as Lent liturgically. The Latin name for Lent, Quadragesima, means "forty" and refers to the forty days Christ spent in the desert which is the origin of the Season. The last two weeks of Lent are known as Passiontide, made up of Passion Week (which begins on Passion Sunday) and Holy Week (which begins on Palm Sunday). The last three days of Holy Week - Maundy Thursday, Good Friday, and Holy Saturday - are known as the Sacred Triduum.
The focus of this Season is the Cross and penance, penance, penance as we imitate Christ's forty days of fasting, like Moses and Elias before Him, and await the triumph of Easter. We fast (see below), abstain, mortify the flesh, give alms, and think more of charitable works. Awakening each morning with the thought, "How might I make amends for my sins? How can I serve God in a reparative way? How can I serve others today?" is the attitude to have.
As we meditate on "The Four Last Things" - Death, Judgment, Heaven, and Hell - we also practice mortifications by giving up something that would be a sacrifice to do without. The sacrifice could be anything from desserts to television to the marital embrace, and it can entail, too, taking on something unpleasant that we'd normally avoid - for example, going out of one's way to do another's chores, performing random acts of kindness, getting out of bed immediately after waking and not dallying under the blankets in the morning, taking cold showers instead of hot ones, etc. (A practice that might help some, especially small children, to think sacrificially is to make use of "Sacrifice Beads" in the same way that St. Thérèse of Lisieux did as a child.) Note, though, that Sundays - even the Sundays of Lent - are not penitential days; they are always celebratory days of rejoicing. So if you've given up sweets for Lent, you can indulge some on Sundays, even during this penitential season (this is why Sundays aren't counted at all as the days "of Lent." If you go by the calendar, Lent seems to last for 46 days - if you count the Sundays. But Catholics don't include those Sundays, so Lent consists of 40 days).
Ideally, the practices one gives up and takes on during Lent should center around eliminating a particular vice, or bad habit, one has, and focus on cultivating the vice's opposite virtue, or good habit. Try to discern which vice you most need to eliminate from your life, and which virtue you need to develop. Let your Lenten sacrifices be those that best help you eradicate your most problematic vice by helping you develop the virtue that defeats it. Provided here is a Lenten Checklist in .pdf format to help you organize your thoughts and Lenten routine: Lenten Checklist.
Don't try to do too much! Do what you're able to do without becoming frustrated or overwhelmed. Carry out your sacrifices without complaint and without making others miserable. And don't make a contest out of your sacrifices; in fact, it's best to keep them to yourself. Another thing to not do is to pretend as if giving up your favorite sin is a proper Lenten sacrifice: sin is something you shouldn't be doing anyway! Yes, most definitely give up that sin - but also add the sacrifice of something good, something allowable, something that is perfectly licit to enjoy in an ordinate way. And as you go along, know that offering up your sufferings for the good of someone you love can help keep you motivated.
Because of the focus on penance and reparation, it is traditional to make sure we go to Confession at least once during this Season to fulfill the precept of the Church that we go to Confession at least once a year; this prepares us to follow the precept of receiving the Eucharist at least once a year during Eastertide. A beautiful old custom associated with Lenten Confession is to, before going to see the priest, bow before each member of your household and to any you've sinned against, and say, "In the Name of Christ, forgive me if I've offended you." One responds with "God will forgive you." Done with an extensive examination of conscience and a sincere heart, this practice can be quite healing (also note that confessing sins to a priest is a Sacrament which remits mortal and venial sins; confessing sins to those you've offended is a sacramental which, like all sacramentals one piously takes advantage of, remits venial sins. Both are quite good for the soul!)
Lent is a particularly good time to otherwise make amends and rebuild broken relationships. Pray for the ability to truly forgive the repentant who've wronged you, and consider those whom you've wronged and whose forgiveness you should seek. Examine your entire life, year by year, looking for ways you've failed, lied, broken God's laws, harmed others, etc. Ask for a contrite and humble heart, and for the fortitude to make right what you've done wrong.
In addition to mortification and charity, seeing and living Lent as a forty day spiritual retreat is a good thing to do. Spiritual reading should be engaged in, over and above one's regular Lectio Divina. Maria von Trapp recommended "the Book of Jeremias and the works of Saints, such as The Ascent of Mount Carmel, by St. John of the Cross; The Introduction to a Devout Life, by St. Francis de Sales; The Story of a Soul, by St. Thérèse of Lisieux; The Spiritual Castle, by St. Teresa of Avila; the Soul of the Apostolate, by Abbot Chautard; the books of Abbot Marmion, and similar works."