On Attention At Prayer
Prayer requires the inseparable presence and co-operation 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.
Attention is a gift of God's grace
The rapt attention which keeps prayer completely free from distraction and from irrelevant thoughts and images is a gift of God's grace. We evince a sincere desire to receive the gift of grace—the soul-saving gift of attention—by forcing ourselves to pray with attention whenever we pray. Artificial attention, as we may call our own unaided attention unassisted by grace, consists in enclosing our mind in the words of the prayer, according to the advice of St. John of the Ladder. If the mind, on account of its newness to the work of prayer, gets out of its enclosure in the words, it must be led back into them again. The mind in its fallen state is naturally unstable and inclined to wander everywhere. But God can give it stability and will do so in His own time in return for perseverance and patience in the practice of prayer. 
Say Prayers Slowly and out loud
Specially helpful in holding the attention during prayer is an extremely unhurried pronunciation of the words of the prayer. Pronounce the words without hurrying so that the mind may quite easily stay enclosed in the words of the prayer, and not slip away from a single word. Say the words in an audible voice when you pray alone; this also helps to hold the attention...
Prayer is all-powerful on account of the all-powerful God Who acts in it. It is the sword of the Spirit, which is the Word of God.  ‘Prayer by its nature is communion and union of man with God; by its action it is the reconciliation of man with God, the mother and daughter of tears, a bridge for crossing temptations, a wall of protection from afflictions, a crushing of conflicts, boundless activity, the spring of virtues, the source of spiritual gifts, invisible progress, food of the soul, the enlightening of the mind, an axe for despair, a demonstration of hope, release from sorrow, the wealth of monks.’ 
At first we must force ourselves to pray. Soon prayer begins to afford consolation, and this consolation lightens the coercion and encourages us to force ourselves. But we need to force ourselves to pray throughout our life,  and few indeed are the ascetics who, on account of the abundant consolation of grace, never need to force themselves.
Prayer acts murderously on our old man, the unregenerate self or nature. As long as it is alive in us, it opposes prayer like death.  Fallen spirits, knowing the power of prayer and its beneficial effect, endeavour by all possible means to divert us from it, prompting us to use the time assigned to prayer for other occupations; or else they try to annul it and profane it with mundane distractions and sinful inattention, by producing at the time of prayer a countless swarm of earthly thoughts, sinful day-dreams and reveries, imaginings and fantasies.
More by Bishop Iganius Brianchaninov
Preparing to Pray
From The Arena: An Offering to Contemporary Monasticism, Chapter 19, by Saint Ignatius (Brianchaninov), translated from the Russian by Archimandrite Lazarus (Jordanville, NY: Holy Trinity Monastery, 1991), pp. 66-78.