Suffice it to say, making more frequent attendance at Mass during the week is an excellent Lenten observance. The point seems so obvious as to not even need a mention, but I wish to mention it nontheless.
The Divine Office
The Divine Office provides a particularly good way -- a liturgical way -- of joining oneself to the rhythm and progression of the liturgical season of Lent -- and all of the rest of liturgical time as well. One prays with the Church's voice, with the proper of the season that the Church presents to us, and with the psalms, canticles and the scriptures generally.
Lent provides a good opportunity to help establish or re-establish the habit of praying the Divine Office by making it a part of your Lenten spiritual discipline and commitments. For those who do not own a breviary proper, various sites are available online for both the older and newer forms of the Roman breviary. For those who would note that they are not yet familiar with how to pray the Divine Office, this may well provide a good opportunity to begin to learn -- which, in its own right, could certainly be understood to be a worthwhile Lenten exercise and discipline that will bear fruit well beyond Lent itself.
Remember as well that praying the Divine Office does not mean praying all of the hours. You might choose Lauds, Vespers and Compline (Morning, Evening and Night prayer), or perhaps simply Lauds and Vespers, or perhaps even only one of the hours. Whatever the case, my suggestion to you is to establish a routine, a discipline for yourself that meshes with your schedule -- and stick to it. Essentially, praying the Divine Office needs to be built into your day to day routine and rhythms. Establishing that routine, that "horarium" if you will, will indeed help you to establish and keep the habit. For example, that might meaning praying Lauds as soon as you awake, or as soon as you have readied yourself for the day; adjust your wake up time by 15 or 20 minutes if need be, and if that seems hard to do, recall the priority we should give to God in our lives and motivate yourself with a consideration of the much greater sacrifice accomplished for our sake on the Cross. It might mean praying Vespers first thing when you return home in the evening from work, or immediately after dinner. Much will depend upon individual schedules of course, both work and family schedules. Wherever it might fit in terms of your day to day routine, make it a part of that routine. By further making it a part of your Lenten commitments, this can be of great motivational help.
A specific practice of spiritual reading that deserves more attention is the practice of "lectio divina" -- the slow, prayerful, meditative reading of the Sacred Scripture defined by four aspects: lectio (the slow reading of some passages of sacred scripture); meditatio (meditating on what has been read); oratio (prayer to God); and contemplatio (the silent adoration and contemplation of the presence of God). Our Holy Father, Pope Benedict XVI, described these stages accordingly in his Message to the Youth of the World on the occasion of the 21st World Youth Day, April 9th, 2006:
...I urge you to become familiar with the Bible, and to have it at hand so that it can be your compass pointing out the road to follow. By reading it, you will learn to know Christ. Note what Saint Jerome said in this regard: "Ignorance of the Scriptures is ignorance of Christ" (PL 24,17; cf Dei Verbum, 25). A time-honoured way to study and savour the word of God is lectio divina which constitutes a real and veritable spiritual journey marked out in stages. After the lectio, which consists of reading and rereading a passage from Sacred Scripture and taking in the main elements, we proceed to meditatio. This is a moment of interior reflection in which the soul turns to God and tries to understand what his word is saying to us today. Then comes oratio in which we linger to talk with God directly. Finally we come to contemplatio. This helps us to keep our hearts attentive to the presence of Christ whose word is "a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts" (2 Pet 1:19).
Pope Benedict has, at other times as well, spoken of and encouraged this practice of lectio divina, noting that he believes the practice can help bring a new spiritual springtime within the Church:
I would like in particular to recall and recommend the ancient tradition of Lectio divina: the diligent reading of Sacred Scripture accompanied by prayer brings about that intimate dialogue in which the person reading hears God who is speaking, and in praying, responds to him with trusting openness of heart (cf. Dei Verbum, n. 25). If it is effectively promoted, this practice will bring to the Church - I am convinced of it - a new spiritual springtime.
Certainly then, this practice might indeed be something to give serious consideration for this Lent -- and beyond.
The Roman Martyrology
The Roman Martyrology presents to us the heroic acts and sufferings of the Christian martyrs, which is certainly pertinent as we bring to mind the Passion of Christ. This presents another possible Lenten consideration. If you do not own a copy, you can read it freely online here.
Other Spiritual Reading
While Lectio Divina or the reading of Sacred Scripture generally, should be of particular consideration for us in the area of spiritual reading, evidently there are other spiritual writings which are certainly of merit as well.
First, in keeping with a liturgical theme, readers may like to consider Dom Prosper Gueranger's writings for Lent.
Two years ago, each day we took readers through the different stational churches of Rome. You are certainly welcome to re-read those entries. You might also want to pick up a copy of The Stational Churches of Rome, written by Fr. Frank Phillips of the Canons Regular of St. John Cantius.
Fast and Abstinence
Lent is traditionally a time of fast and abstinence. Evidently, the obligations surrounding this have been much relaxed in the West in the past few decades, but the relaxing of the obligation does not mean there is not value in still opting to pursue these practices. Indeed, there is nothing (outside of health and age) to prevent one from taking up the practice of devotional fasts and abstinence.
Shortly after Lent begins, we traditionally observe the Lenten Ember days -- on Wednesday, February 29th, Friday, March 2nd and Saturday, March 3rd. Whether you do or don't follow the EF calendar, these days might provide a particularly good opportunity to observe the fast and abstinence discipline.
Each of these suggestions are all things which are not only pertinent to Lent, but also beyond Lent. Indeed, I would encourage you to make it your intent to continue them beyond Lent and through the rest of the liturgical year.