Do not attempt to assess the quality of your prayer. God alone can judge its value. To us, our own prayer must always appear so poor an effort, so inadequate an achievement, that the cry of the publican spontaneously rises from our lips.
When you are praying alone, and your spirit is dejected, and you are wearied and oppressed by your loneliness, remember then, as always, that God the Trinity looks upon you with eyes brighter than the sun; also all the angels, your own Guardian Angel, and all the Saints of God. Truly they do; for they are all one in God, and where God is, there are they also. Where the sun is, thither also are directed all its rays. Try to understand what this means.
When praying, endeavor by every means to feel in your heart the truth and the power of the words of the prayer; feed yourself upon them as upon an imperishable food; water your heart with them as with a dew; and warm yourself by them as by means of a beneficial fire.
Until we have acquired true prayer, we are like those who introduce children to walking. Make the effort to raise up, or rather, to enclose your mind within the words of your prayer; and if, like a child, it gets tired and falters, raise it up again. The mind, after all, is naturally unstable, but the God Who can do everything can also give it firm endurance. Persevere in this, therefore, and do not grow weary...
When said with pain, the prayer gives birth to mourning. Mourning brings tears. Tears in turn give birth to purer prayer. For tears like a fragrant myrrh wash away the filth, and thus the inbreathing of God is cleansed, which like a dove is confined within four walls, as if made of the four elements.... And then, as soon as the walls break down and collapse, the dove immediately flies to the Father whence it came.
'If our prayer is not in harmony with our deeds, we labor in vain,' Abba Moses often told the young monks. 'How are we to accomplish such harmony?' they asked him one day. 'When we make that which we seek fitting to our prayer,' explained the saint. 'Only then can the soul be reconciled with its Creator and its prayer be acceptable, when it sets aside all of its own evil intentions.'
Whether you pray with brethren or alone, try to pray not simply as a routine, but with conscious awareness of your prayer. Conscious awareness of prayer is concentration accompanied by reverence, compunction and distress of soul as it confesses its sin with inward sorrow.
When you are praying, don’t rack your brains to find words. On many occasions the simple, monotonous stammering of children has satisfied their Father who is in heaven. Don’t bother to be loquacious lest the mind is bewildered in the search for words. The tax-collector gained the Lord’s forgiveness with a single sentence, and a single word charged with faith was the salvation of the robber. Loquacity in prayer often fills the head with foolish fancies and provokes distractions. Brevity on the other hand - sometimes only one word is enough - in general favors recollection.
The one who prays ought never to halt his movement of sublime ascent toward God. For just as we should understand the ascent 'from strength to strength' as the progress in the practice of the virtues, 'from glory to glory' (2 Cor. 3:18) as the advance in the spiritual knowledge of contemplation, and the transfer from the letter of sacred writing to its spirit, so in the same way the one who is settled in the place of prayer should lift his mind from human matters and the attention of the soul to more divine realities.
Prayer is a great good if offered up from a thankful soul; if we are steadfast in it, so that whether we receive or do not receive what we pray for we at all times give thanks to God. For since He will sometimes grant what we ask and sometimes will not, in both cases it is to our gain... For oftentimes God will delay, not as denying our prayer, but in His wisdom seeking rather for our perseverance, and desiring to draw us nearer to Himself; as a loving father when asked by his son for something will often do; withholding consent, and not from the will to refuse, but rather to encourage him in steadfastness.
Ask the angels and the saints to intercede for you, just as you'd ask people who are alive. Stand face to face with them, in the belief that they are also standing face to face with you.