Taken from Mediator Dei:

194. We also exhort you, Venerable Brethren, to promote with care congregational singing, and to see to its accurate execution with all due dignity, since it easily stirs up and arouses the faith and piety of large gatherings of the faithful. Let the full harmonious singing of our people rise to heaven like the bursting of a thunderous sea[176] and let them testify by the melody of their song to the unity of their hearts and minds[177], as becomes brothers and the children of the same Father.
195. What We have said about music, applies to the other fine arts, especially to architecture, sculpture and painting. Recent works of art which lend themselves to the materials of modern composition, should not be universally despised and rejected through prejudice. Modern art should be given free scope in the due and reverent service of the church and the sacred rites, provided that they preserve a correct balance between styles tending neither to extreme realism nor to excessive "symbolism," and that the needs of the Christian community are taken into consideration rather than the particular taste or talent of the individual artist. Thus modern art will be able to join its voice to that wonderful choir of praise to which have contributed, in honor of the Catholic faith, the greatest artists throughout the centuries. Nevertheless, in keeping with the duty of Our office, We cannot help deploring and condemning those works of art, recently introduced by some, which seem to be a distortion and perversion of true art and which at times openly shock Christian taste, modesty and devotion, and shamefully offend the true religious sense. These must be entirely excluded and banished from our churches, like "anything else that is not in keeping with the sanctity of the place."[178]
196. Keeping in mind, Venerable Brethren, pontifical norms and decrees, take great care to enlighten and direct the minds and hearts of the artists to whom is given the task today of restoring or rebuilding the many churches which have been ruined or completely destroyed by war. Let them be capable and willing to draw their inspiration from religion to express what is suitable and more in keeping with the requirements of worship. Thus the human arts will shine forth with a wondrous heavenly splendor, and contribute greatly to human civilization, to the salvation of souls and the glory of God. The fine arts are really in conformity with religion when "as noblest handmaids they are at the service of divine worship."[179]
197. But there is something else of even greater importance, Venerable Brethren, which We commend to your apostolic zeal, in a very special manner. Whatever pertains to the external worship has assuredly its importance; however, the most pressing duty of Christians is to live the liturgical life, and increase and cherish its supernatural spirit.
198. Readily provide the young clerical student with facilities to understand the sacred ceremonies, to appreciate their majesty and beauty and to learn the rubrics with care, just as you do when he is trained in ascetics, in dogma and in a canon law and pastoral theology. This should not be done merely for cultural reasons and to fit the student to perform religious rites in the future, correctly and with due dignity, but especially to lead him into closest union with Christ, the Priest, so that he may become a holy minister of sanctity.
199. Try in every way, with the means and helps that your prudence deems best, that the clergy and people become one in mind and heart, and that the Christian people take such an active part in the liturgy that it becomes a truly sacred action of due worship tO the eternal Lord in which the priest, chiefly responsible for the souls of his parish, and the ordinary faithful are united together.
200. To attain this purpose, it will greatly help to select carefully good and upright young boys from all classes of citizens who will come generously and spontaneously to serve at the altar with careful zeal and exactness. Parents of higher social standing and culture should greatly esteem this office for their children. If these youths, under the watchful guidance of the priests, are properly trained and encouraged to fulfill the task committed to them punctually, reverently and constantly, then from their number will readily come fresh candidates for the priesthood. The clergy will not then complain -- as, alas, sometimes happens even in Catholic places -- that in the celebration of the august sacrifice they find no one to answer or serve them.
201. Above all, try with your constant zeal to have all the faithful attend the eucharistic sacrifice from which they may obtain abundant and salutary fruit; and carefully instruct them in all the legitimate ways we have described above so that they may devoutly participate in it. The Mass is the chief act of divine worship; it should also be the source and center of Christian piety. Never think that you have satisfied your apostolic zeal until you see your faithful approach in great numbers the celestial banquet which is a sacrament of devotion, a sign of unity and a bond of love.[180]