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.
Pray firstly to be purified of passions, secondly to be freed from ignorance and forgetfulness, and thirdly to be delivered from all temptation and forsaking.
O man, learn the humility of Christ and the Lord will give you to taste of the sweetness of prayer. And if you would pray cleanly, be humble and temperate, confess yourself thoroughly, and prayer will feel at home in you. Be obedient, submit with a good conscience to those in authority; be content with all things, and your mind will be cleansed of vain thoughts. Remember that the Lord sees you, and be fearful lest you anywise offend your brother, whom neither dispraise nor grieve, even by a look, and the Holy Spirit will love you and will Himself be your help in all things.
Unless humility and love, simplicity and goodness regulate our prayer, this prayer - or, rather, this pretence of prayer - cannot profit us at all. And this applies not only to prayer, but to every labor and hardship undertaken for the sake of virtue.
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...
How can one avoid distractions in prayer? If one abides in the presence of God. Indeed, when in the presence of one's judge and one's master, and speaking with him, one does not let one's eyes wander elsewhere. How much more should the one who approaches the Lord never turn away the eye of his heart, but fix it on Him who searches the reins and the heart.
You describe how bitterly you regret the inefficacy of your prayers. Beware: to wish for consolation or revelation in prayer is a sure sign of pride. Pray humbly, in perfect simplicity, seeking salvation only through forgiveness, & having faith that God will extend to you His mercy - as He did to the publican.
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.
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.
Both public and private prayer are necessary in order that we may lead a truly Christian life, and that the life of the spirit should not become extinct in us. It is indispensable that we should attend divine service in church with faith, zeal and understanding, just as it is indispensable to provide a lamp with fuel or power if it is to burn and not to go out.
Prayer requires the inseparable presence and cooperation of the attention. With attention, prayer becomes the inalienable property of the person praying; in the absence of attention, it is extraneous to the person praying. With attention, it bears abundant fruit; without attention, it produces thorns and thistles. The fruit of prayer consists in illumination of mind and compunction of heart; in the quickening of the soul with the life of the Spirit. Thorns and thistles are a sign of deadness of soul and pharisaical self-esteem which springs from the hardening of a heart which is contented and elated by the quantity of the prayers and the time spent in reciting those prayers.
And when you pray, see that you ask not for what is alien to your life, and provoke the Lord. Ask not for money, not for human glory, nor power, nor for any of the things that pass away. But seek for the kingdom of God, and all that is needed for your body will be provided; as the Lord Himself has said: Seek ye the kingdom of God, and his justice, and all these things will be added unto you (Matthew 6:33).
Tedium is the granddaughter of despondency, and the daughter of slothfulness. In order to drive it away, labor at your work, and do not be slothful in prayer. The tedium will pass, and zeal will come. And if to this you add patience and humility, then you will be rid of all misfortunes and evils.