Musar su Salmi 33:14

One should accustom himself that his prayer be with great intent, and if he cannot empty his heart of unworthy thoughts, let him seek a way. For example, let him think at the time of his prayers that the Creator is standing opposite him and looking at every outward expression of his lips, as it is said (Psalms 33:14), “From the place of His habitation He looketh intently upon all the inhabitants of the earth.” If a man believes this, he will have fear and will empty his heart. He should close his eyes when he prays, for this will help him in the matter of intent, and at all times let his garments be white and let him firmly intend that his body be clean and pure of all uncleanliness. If he draws near to his wife and washes and cleanses his body afterwards, he will be doing an intelligent thing. For the cleanliness of the body renews the cleanliness of the heart; and similarly, the soiling of the body soils the heart, and let him resolve that in the matter of his prayer he will be among the first to enter and among the last to leave. Let his prayer be with gentleness of spirit and with a contrite heart. Let him not be like the crane who speaks but does not know what it is saying. But he should keep watch over the words that leave his mouth and concentrate his mind on their meaning. Let his prayer not be like a body without a soul, for the words are like the body, and their meaning is like the soul. When the one who prays does not pay close attention to them, they are a body without a soul, and the soul which is within man must not approach the Creator with empty words but with meaningful words, and he should be like an angel in his prayer wrapped in his tallit and adorned with tefillin. When he sees and discerns in himself that he is like an angel, it would be shameful in his eyes to stretch forth his hand to commit sins or evil deeds.