How to pray

Luke 11:1-13

There are two kinds of prayer, one composed of praise with humility, the other of petitions, and more subdued. Then whenever you pray, do not first break forth into petition; but if you condemn your inclination, supplicate God as if you were forced. And when you begin to pray, forget all visible and invisible creatures, but commence with the praise of Him who created all things.

See how great a preparation you need, to be able to say boldly to God, "O Father", for if you have your eyes fixed on worldly things and utter this prayer, we can imagine God saying, "Do you that are of a corrupt life call the Author of the incorruptible your Father? Why do you defile the pure Name by your foul speech? If You were my child, my own attributes should have defined your way of life. I do not recognize in you the image of my nature. Our traits and qualities are opposite."

Since Jesus said that the life of man after the resurrection will be like to that of Angels (Lk 20:36), it follows, that our life in this world should be so ordered with respect to that which we hope for hereafter, that living in the flesh we may not live according to the flesh. It is here the true Physician of the souls destroys the nature of the disease, that those who have been seized with sickness, whereby they have departed from the Divine will, may forthwith be released from the disease by being joined to the Divine will. For the health of the soul is the due fulfillment of the will of God.

Our Savior then gives us a very necessary piece of instruction. For oftentimes we rashly, from the impulse of pleasure, give way to hurtful desires. When we ask any such thing from God, we shall not obtain it. For when your son asks you for bread, you give it him gladly, because he seeks a wholesome food. But when from lack of understanding he asks for a stone to eat, you don't give in, but rather hinder him from satisfying his hurtful desire. So that the sense may be, "But which of you asking his father for bread, (which the father gives,) will he give him a stone? (if he asked it.)"

Reference:
Catena Aurea (St. Thomas Aquinas)
Monastic Constitutions (St. Basil the Great)
Homily #2 on the Lord's Prayer (St. Gregory of Nyssa)
Homily #3 on the Lord's Prayer (St. Gregory of Nyssa)
Homily #4 on the Lord's Prayer (St. Gregory of Nyssa)
Commentary on Luke, Sermon #79 (St. Cyril of Alexandria)