1. WHAT IS PRAYER? 
St. John Damascene defines prayer as “the raising of one's mind and heart to God or the requesting of a suitable good,"  while St John Climacus views it as an “intimate conversation and union with God." 
Prayer is absolutely necessary for our spiritual life. It is, as it were, the “breathing" that permits the life of the spirit to develop. In prayer, our faith in God's presence and love is affirmed. Prayer fosters hope, which leads to directing our life towards God and trusting in his providence. It expands our heart to respond with love to divine Love.
Prayer issues from the very depths of our soul, from the “heart" (cf. Catechism 2562). We are led by the Holy Spirit to unite ourselves to Christ, teacher, model and path for all Christian prayer (cf. Catechism 2599 ff.), and with Christ, through Christ and in Christ, we are drawn to God the Father, coming to share in the riches of the life of the Trinity (cf. Catechism 2559-2564). Hence the importance of the liturgy and, at its center, the Eucharist, in the life of prayer.
2. CONTENT OF PRAYER
As in any conversation of love, the topics of prayer are many and varied, but a few particularly important ones should be highlighted.
Sacred Scripture contains many references to supplicatory prayer. Jesus himself had recourse to it, and taught us the importance of simple and trusting petition. Christian tradition has echoed Christ's invitation to beseech God for help in many different ways: asking for pardon, asking for one's own and others' salvation, praying for the Church, the apostolate, needs of all sorts, etc.
Prayer of petition is part of mankind's universal religious experience. Recognizing even vaguely the reality of God (or more generally, a superior being) leads to turning to him and asking for his protection and help. Prayer is certainly not limited to supplication, but petitioning God for help is a clear recognition of our condition as creatures and our absolute dependence on God, whose love for us is revealed in its fulness through faith (cf. Catechism 2629-2635).
Recognizing all the gifts we have received and, through them, God's mercy and generosity, spurs us to turn our hearts to God in thanksgiving. From beginning to end, Sacred Scripture and the history of spirituality is imbued with an attitude of thanksgiving.
In the light of faith, we come to realize that whatever happens to us forms part of God's loving plan, and that everything works for the good of those who love God (cf. Rom 8:28). “Make it a habit to raise your heart to God, in acts of thanksgiving, many times a day. Because He bestows on you various gifts. Because you've been despised. Because you don't have what you need, or because you do have it. Because He made his Mother, who is also your Mother, so beautiful. Because He created the sun and the moon and an animal or plant of this or that kind. Because He made that man eloquent and you He left slow of speech… Thank Him for everything, because everything is good." 
Adoration and praise
An essential part of prayer is recognizing and proclaiming God's grandeur, the plenitude of his being, his infinite goodness and love. Consideration of the beauty and immensity of the universe prompts us to praise him, as we see in many biblical texts (cf., for example, Ps 19; Sir 42:15-25; Dan 3:32-90), and in traditional Christian prayers.  Praise may be prompted also by the great and wonderful works that God performs in the history of salvation, as shown by the Magnificat ( Lk 1:46-55) and the great Pauline hymns (see, for example, Eph 1:3-14), or by the small and even tiniest details that manifest God's love.
In any case, what characterizes praise is that it focuses our attention directly on God himself, as he is in himself, in his unlimited and infinite perfection. “Praise is the form of prayer which recognizes most immediately that God is God. It lauds God for his own sake and gives him glory, quite beyond what he does, but simply because HE IS" ( Catechism 2639). Therefore it is closely united to adoration, to the deeply-felt realization of the smallness of all created reality in comparison with the Creator, and, as a consequence, to humility, to accepting our personal littleness before the One who infinitely transcends us. And we are led to marvel at the fact that this God of ours, to whom the angels and the whole universe render homage, deigned not only to turn his regard to man but also to dwell in man, and even more, to become incarnate.
Adoration, praise, petition and thanksgiving are the basic dispositions underlying all dialogue between man and God. Whatever the particular content of our prayer, everyone who prays always does so, explicitly or implicitly, by adoring, praising, beseeching or giving thanks to God, whom we revere, love and trust. At the same time it is worth repeating that the specific content of prayer can vary considerably. Our prayer may sometimes involve considering passages from Scripture, or going more deeply into some Christian truth, or reliving Christ's life, or drawing close to our Lady…. Or it may involve starting from events in our own life to share with God our joys and worries, our hopes and problems; or to seek his support and consolation; or to examine in God's presence our own behavior and make resolutions and decisions; or simply to talk about the events of the day with someone whom we know loves us.
“You write: 'To pray is to talk with God. But about what?' About what? About Him, about yourself: joys, sorrows, successes and failures, noble ambitions, daily worries, weaknesses! And acts of thanksgiving and petitions: and Love and reparation. In a word: to get to know him and to get to know yourself: 'to get acquainted!'"  In one way or another, prayer will always be an intimate and filial meeting with God, which will foster our sense of God's closeness, and lead to living each day in God's presence.
3. WAYS OR FORMS OF PRAYING
Regarding the ways or forms of praying, spiritual writers usually make various distinctions: vocal prayer and mental prayer; public and private prayer; predominantly intellectual or reflective prayer and affective prayer; guided and spontaneous prayer, etc. Sometimes these writers try to outline a gradation of intensity in prayer, distinguishing between mental prayer, affective prayer, the prayer of quietude, contemplation, unitive prayer….
The Catechism distinguishes between vocal prayer, meditation and the prayer of contemplation. These three “have one basic trait in common: composure of heart. This vigilance in keeping the Word and dwelling in the presence of God makes these three expressions intense times in the life of prayer" (Catechism 2699). The Catechism makes clear that the use of this terminology is not meant to refer to three levels in the life of prayer but rather to two ways of praying, vocal prayer and meditation, presenting both as apt to lead to contemplation, the summit of the life of prayer. In our discussion below we will follow this approach.
“Vocal prayer is an essential element of the Christian life. To his disciples, drawn by their Master's silent prayer, Jesus teaches a vocal prayer, the Our Father. He not only prayed aloud the liturgical prayers of the synagogue but, as the Gospels show, he raised his voice to express his personal prayer, from exultant blessing of the Father to the agony of Gesthemani" (Catechism 2701). We could define vocal prayer as prayer that makes use of set words, whether short formulas (aspirations), words taken from Scripture, or prayers from traditional spirituality (the Veni Sancte Spiritus , the Salve , the Memorare ....).
It is important to stress that vocal prayer is not just a matter of words but above all of the intellect and the heart. If this devotion is lacking, if there is no awareness of Who is being addressed in the prayer and what is being prayed for, then, as St Teresa of Jesus graphically puts it, one cannot properly speak of prayer “however much the lips wag." 
Vocal prayer plays a decisive role in teaching people how to pray, especially when first starting to talk to God. Through learning the sign of the Cross and vocal prayers, children—and often adults as well—take their first steps in living the faith in practice, and thus in their life of prayer. However, the role and importance of vocal prayer is not restricted to the beginning of one's dialogue with God, but is meant to accompany every stage in our spiritual development.
Meditation means applying our mind to the consideration of a reality with the desire to know and understand it in greater depth. For a Christian, meditation (often called “mental prayer") involves directing our thoughts to God as he revealed himself during the history of Israel and definitively and fully in Christ. And then, with the light we receive from God, turning to our own life to appraise and adapt it to the mystery of life, communion and love that God has opened our eyes to.
Meditation may develop spontaneously, during moments of silence accompanying or following liturgical celebrations or occasioned by reading some biblical text or a passage from some spiritual writer. At other moments it can be limited to times specifically dedicated to it. In any case, it is obvious that, especially at the beginning but not only then, it requires effort, the desire to deepen our knowledge of God and the requirements of his will, and to persist in our determination to truly improve in our Christian life. In this sense, it can be said that “meditation is above all a quest" (Catechism 2705), although we should stress that it is not a matter of seeking something but Someone . The aim of Christian meditation is not only, or primarily, to understand something (in the final analysis, to grasp God's ways of acting and manifesting himself), but to draw close to him, to identify ourselves with his will and to be in union with him.
As one's experience of Christian life grows, and with it, one's prayer life, a more constant, personal and intimate communion between the believer and God comes about. Prayer at this level is what the Catechism calls “contemplative" prayer. Based on a lively sense of God's loving nearness, this form of prayer transcends formal words and concepts and leads to truly living in intimate communion with him.
“What is contemplative prayer?" the Catechism asks at the beginning of the section dealing with contemplative prayer. And it answers with words taken from St Teresa of Jesus: it is simply “a close sharing between friends; it means taking time frequently to be alone with him who we know loves us."  “Contemplative prayer seeks him 'whom my soul loves' (Song 1:7). It is Jesus, and in him, the Father. We seek him, because to desire him is always the beginning of love, and we seek him in that pure faith which causes us to be born of him and to live in him" ( Catechism 2709).
“Contemplative prayer is the prayer of the child of God, of the forgiven sinner who agrees to welcome the love by which he is loved and who wants to respond to it by loving even more. But he knows that the love he is returning is poured out by the Spirit in his heart, for everything is grace from God. Contemplative prayer is the poor and humble surrender to the loving will of the Father in ever deeper union with his beloved Son" (Catechism 2712).
This form of prayer can come about during specific moments dedicated to prayer or at any other moment. In short, prayer is destined to encompass the entire human person—intellect, will and feelings—and to reach the center of the heart and change its dispositions, shaping the Christian's whole being, making each one another Christ (cf. Gal 2:20).
4. CONDITIONS AND CHARACTERISTICS OF PRAYER
An important condition for true prayer is recollection . The term “recollection" means the action whereby the will, by virtue of its capacity to control all the tendencies involved in human nature, tries to moderate its inclination to dispersion, fostering interior calm and serenity. During moments dedicated especially to prayer, this attitude of leaving aside other tasks and trying to avoid distractions is essential, but it is by no means limited to those moments. Rather, it should spread to other moments of one's day until recollection becomes habitual, filling the heart with a spirit of faith and love that leads us to strive to carry out all our activities, implicitly or explicitly, with reference to God, even when engaged in work that demands our whole attention.
Another condition for prayer is trust . Without full trust in God and his love for us prayer is impossible, at least sincere prayer capable of overcoming trials and difficulties. It is not just a matter of trusting that a certain petition will be granted, but rather of the assurance that the One we are speaking to loves us and understands us, and that we can open our heart to him without reserve (cf. Catechism 2734-2741).
Sometimes prayer is a spontaneous dialogue arising from the depth of the soul that brings joy and consolation. At other time however—perhaps more frequently—it calls for determination and perseverance. Then a feeling of discouragement may creep in leading one to think that it does not make sense spending time talking with God (cf. Catechism 2728). Moments like these make clear the importance of another condition for prayer: perseverance . The goal of prayer is not to obtain favors or consolations, but rather communion with God, whence the importance of persevering in prayer, which is always—whether filled with sensible feelings or not—a living encounter with God (cf. Catechism 2742-2745, 2746-2751).
A fundamental trait of all Christian prayer is its Trinitarian character. The Holy Spirit infuses faith, hope and charity into our hearts and leads us to Christ, the incarnate Son of God, in whose humanity we perceive the divinity of his Person. Following this path, we come to God the Father, and to an ever more trusting relationship with him. Christian tradition also recommends going to the intercession of the angels and saints, and especially to Mary the Mother of God.
Thus Christian prayer is an eminently filial prayer. It is the prayer of sons or daughters who—whether joyful or suffering, working or resting—turn to their Father with simplicity and sincerity and place in his hands all their concerns, finding there welcome and a love that gives meaning to everything.
José Luis Illanes
Catechism of the Catholic Church , 2558-2758.
St Josemaria, “Christ Triumphs through Humility," “The Eucharist, Mystery of Faith and Love," “The Ascension of Our Lord," “The Great Unknown," “To Jesus through Mary," in Christ is Passing By , 12-21, 83-94, 117-126, 127-138 and 139-149.
“Getting to Know God," “A Life of Prayer," “Towards Holiness," in Friends of God , 142-153, 238-257, 294-316.
Javier Echevarria, Paths to God , ch. 8, “Along the Paths of Prayer," Scepter.
 “ Great is the mystery of the faith! The Church professes this mystery in the Apostles' Creed (Part One ) and celebrates it in the sacramental liturgy ( Part Two ), so that the life of the faithful may be conformed to Christ in the Holy Spirit to the glory of God the Father ( Part Three ). This mystery, then, requires that the faithful believe in it, that they celebrate it, and that they live from it in a vital and personal relationship with the living and true God. This relationship is prayer" (Catechism , 2558).
 St John Damascene, De fide orthodoxa , III, 24; PG 94,1090.
 St John Climacus, Scala paradisi , 28; PG 88, 1129.
 St Josemaria, The Way , 268.
 Two of the best known are “Glory to God in the highest" and the “Canticle of Brother Sun and Sister Moon" by St Francis of Assisi.
 St Josemaria, The Way , 91.
 St Teresa of Jesus, Foundations , ch. 1, 7.
 St Teresa of Jesus, Life , ch. 8, no. 5; cf. Catechism , 2709.