Taken from the Catechism of Saint Pius X: The Way to Assist at Mass

15 Q. What is required in order to assist at Holy Mass well and profitably? 

A. To assist at Holy Mass well and profitably two things are necessary: (1) Modesty of person and (2) Devotion of heart. 

16 Q. In what does modesty of person consist? 

A. Modesty of person consists especially in being modestly dressed, in observing silence and recollection and, as far as possible, in remaining kneeling, except during the time of the two Gospels which are heard standing. 

17 Q. In hearing Holy Mass which is the best way to practice true devotion? 

A. In hearing Holy Mass the best way to practice true devotion is the following: 

(1) From the very beginning to unite our intention with that of the priest, offering the Holy Sacrifice to God for the ends for which it was instituted. 

(2) To accompany the priest in each prayer and action of the Sacrifice. 

(3) To meditate on the Passion and Death of Jesus Christ and to heartily detest our sins, which have been the cause of them. 

(4) To go to Communion, or at least to make a spiritual Communion while the priest communicates. 

18 Q. What is spiritual Communion? 

A. Spiritual Communion is a great desire to be united sacramentally with Jesus Christ. saying, for example: "My Lord Jesus Christ, I desire with my whole heart to be united with Thee now and forever;" and then make the same acts that are to be made before and after sacramental Communion. 

19 Q. Does the recitation of the Rosary or other prayers during Mass prevent us from hearing it with profit? 

A. The recitation of the Rosary and other prayers during Mass does not prevent us from hearing it with profit, provided we try as far as possible to ollow the parts of the Holy Sacrifice. 

20 Q. Is it advisable to pray for others while assisting at Mass? 

A. Yes it is advisable to pray for others while assisting at Mass; nay more, the time of Holy Mass is the most suitable of all times to pray for the living and the dead. 

21 Q. What should we do after Mass? 

A. After Mass we should give God thanks for having allowed us to assist at this great Sacrifice, and we should ask pardon for all the faults we may have committed while assisting at it.