I found this masterpiece on prayer entitled: “Let your prayer come from a humble heart” from a ” treatise on the Lord’s Prayer by Saint Cyprian, bishop and martyr of the 3rd century, very inspiring:

When we pray, our words should be calm, modest and disciplined. Let us reflect that we are standing before God. We should please him both by our bodily posture and the manner of our speech. It is characteristic of the vulgar to shout and make a noise, not those who are modest. On the contrary, they should employ a quiet tone in their prayer. Moreover, in the course of this teaching, the Lord instructed us to pray in secret. Hidden and secluded places, even our own rooms, give witness to our belief that God is present everywhere; that he sees and hears all; that in the fullness of his majesty, he penetrates hidden and secret places.
The same modesty and discipline should characterize our liturgical prayer as well. When we gather to celebrate the divine mysteries with God’s priest, we should not express our prayer in unruly words; the petition that should be made to God with moderation is not to be shouted out noisily and verbosely. For God hears our heart not our voice. He sees our thoughts; he is not to be shouted at.

Anna maintained this rule; in her observance of it she is an image of the Church. In the First Book of Kings we are told that she prayed quietly and modestly to God in the recesses of her heart. Her prayer was secret but her faith was evident. She did not pray with her voice, but with her heart, for she knew that in this way the Lord would hear her. She prayed with faith and obtained what she sought. Scripture makes this clear in the words: She was speaking in her heart; her lips were moving but her voice could not be heard; and the Lord heard her prayer.

My friends, anyone who worships should remember the way in which the tax-collector prayed in the temple alongside the Pharisee. He did not raise his eyes immodestly to heaven or lift up his hands arrogantly. Instead he struck his breast and confessing the sins hidden within his heart he implored the assistance of God’s mercy. While the Pharisee was pleased with himself, the tax-collector deserved to be cleansed much more because of the manner in which he prayed. For he did not place his hope of salvation in the certainty of his own innocence; indeed, no one is innocent. Rather he prayed humbly, confessing his sins. And the Lord who forgives the lowly, heard his prayer”