Anyone can use the Jesus prayer. It can be said at any time. To begin saying the prayer as part of our daily prayer rule we must follow the direction of Jesus. He says, "Come ye yourselves apart into a desert place, and rest awhile" (Mark 6:31); "Study to be quiet" (I Thess. 4: 11); then pray in secret—alone and in silence. Select a place where it will be quiet and you will not be disturbed. It is best if you can protect the senses from as much stimulation as possible. It is best to pray the Jesus Prayer early in the morning before sunrise when the mind is at rest and undistracted, the body is relaxed and there is little activity to disturb your concentration. Some may find the evening to work better.
Before you start think about who you are about to address. Make the sign of the cross and a few prostrations with the feeling of contrition and sorrow for your sinfulness. Select a comfortable position for prayer. Gently shut your eyes like the closing of tired eyes of a child falling to sleep. Set aside all your worldly cares telling yourself you will have plenty of time for them after you pray. Relax your body.
After you have quieted yourself begin by praising God with Glory to you.., Our Heavenly King Comforter…, the Trisagion prayer, 51st Psalm, and the Creed. Then you can begin to say the Jesus Prayer out loud, loud enough so the ears can hear it, slowly and concentrating on the meaning of the words. “The words of the prayer ought to be said without the least hurry, even lingering, so that the mind can lock itself into each word…” (Saint Ignatius Brianchaninov)
Slowly say,
Lord …. Jesus Christ …. Son of God …. Have Mercy …. on Me …. a Sinner. 
Try to keep your mind from escaping from its total concentration on the words. It will try just like a cornered or caged wild animal continually seeks to find a way out. The body is not accustomed to be under the control of the soul. When you reach the end of the prayer immediately begin to say it again. Make it like a continuous chain. The spacing of the words must fit your own make-up. Some will want to go very slow and others a little faster. The aim, with awe of God and contrition, is to concentrate your mind on the words and let them drop into your heart like drops of water slowly dripping from a leaky faucet.. Let the prayer resonate in your ears and in the area of your heart, savor each word with love, becoming totally absorbed in the words. You need to feel the words being absorbed within. Feel a contriteness in your heart because of your missing the make that God has set for you by creating you in His image. Feel the unconditional love of His unlimited mercy. If you go too fast you lose this feeling. If you go too slow you lose the content of the prayer. Say it slowly and deliberately. You do not want to rush as you are engaged in something important and potentially dangerous. You need to harness the wildness of your biological brain. Its like an automobile racing down the road at 80 miles per hour and is much more difficult to control than one cruising at twenty-five. Slow it down. Operate at the twenty-five miles per hour speed when you start - take it slow and deliberately finding the pace that bests suits you so the prayer can penetrate the inner depths of your heart in silence.
Saint Ignatius Brianchaninov says, “at first, the words should be pronounced with extreme unhurridness so that the mind may have time to enter the words as forms… One must train oneself to it as if one were reading syllables” (On the Prayer of Jesus, p 56). St. John of the Ladder counsels that the mind should be locked into the words of the prayer and should be forced back each time it departs from it (Step XXVIII, ch. 17). Do not be disturbed if the words do not drop smoothly and are interrupted by thoughts, images, and feelings in the beginning. It takes some effort to tame the mind that is controlled by the brain. Eventually, the words will drop effortlessly into your heart. You need to focus intently and concentrate on the prayer. Much effort is required in the beginning.
Keep Focused on the Words of the Prayer
Avoid any association with words of the prayer. Don’t try to visualize the human person of Jesus or any other image. Don’t try and take a diversionary path by letting your mind go into the life of Jesus or any theological questions. Don’t reflect on the details of your sinfulness or try to solve any of your problems. Simply hold in your heart, with total humility, the awe of God and a feeling of contriteness. Keeping focused on the words of the prayer is very important because the mind can very quickly diverge from them to mundane day-to-day activities and when this happens you have lost your focus on God. If this happens, you are back in your own sea of worldly cares and distracted from your prayer. You will most assuredly be distracted this way during prayer. Concentrate on God who lives in the depths of your heart as Saint Theophan says,
“The essential part is to dwell in God, and this walking before God means that you live with the conviction ever before your consciousness that God is in you, as He is in everything: you live in the firm assurance that He sees all that is within you, knowing you better than you know yourself. This awareness of the eye of God looking at your inner being must not be accompanied by any visual concept, but must be confined to a simple conviction or feeling.”(Art of Prayer, p 100)
Attention of the Mind Essential
You can expect to be bombarded with thoughts like a swarm of gnats. When your mind is distracted from the prayer by thoughts, and it will, be polite and gentle but firmly nudge your mind back to the concentration on the prayer and seeking God. When you recognize your mind is wandering do not let it continue on this path. Don’t accept even good thoughts. Let your soul take charge and move your focus back to the words of the prayer. It is important to recognize when you are being distracted by thoughts which may occur at the same time as you are saying the prayer. They climb on top of your words and ride piggyback on them. If you don’t intercede to bring your attention back to your prayer exclusively, you will not progress in your aim to come closer to God. When this happens your prayer is no longer sincere but only mechanical. Allow the Spirit working in your soul bring you back to the prayer and continue saying it with sincerity and feeling.
Saint John of the Ladder puts it this way,
Try to restore, or more exactly, to enclose your thought in the words of the prayer. If on account of its infancy, it wearies and wanders, lead it again. The mind is naturally unstable. But He Who orders all things can control it. If you acquire this practice and constantly retain it, He who sets the bounds of the sea of your mind will say to it during your prayer: Hitherto thou shalt come, and shalt go no further (Job 38:11). It is impossible to bind a spirit. But where the Creator of that spirit is present, there everything obeys Him. (Ladder 28:17)
When the devil sees us trying to pray, he works hard to distract us. He seeks out our weaknesses and generates all kinds of thoughts to distract us Quite often the thoughts that come to us during prayer are related to our weaknesses, the areas where our passions have great influence in our lives. Outside of prayer we can use this information to confront these weaknesses. Do let your mind begin to analyze this during your prayer.
more on controlling the mind...
The Heart 
Our attention must be concentrated on the heart and not on the brain. You should feel the action of the Jesus Prayer on your heart. You will feel a warmth. It is important to realize that we love God first with our hearts and then with our mind. Our present condition has this reversed. This is what we are trying to correct through our practice of the prayer. We aim to open our heart and feel the sting of our repentance. You may feel some soreness initially around the heart. Don’t mind this just keep your attention focused on the prayer. There are some people who have thought they have been afflicted with heart disease and go visit doctors who can find nothing wrong. It is a pain similar to those you have when exercising after a period of no exercise. It is the pain of grace you are feeling. (A Night in the Desert of the Holy Mountain, pp 84-86)
Remember, this is a process and you will go through stages. Saint Ignatius Brianchaninov reminds us that our simple attentive beginnings lead us to the temple of the heart.
It is one thing to pray with attention with the participation of the heart; it is another thing to descend with the mind into the temple of the heart and from there to offer mystical prayer filled with divine grace and power. The second is a result of the first. The attention of the mind during prayer draws the heart into sympathy. With the strengthening of the attention, sympathy of heart and mind is turned into union of heart and mind. Finally, when the attention makes the prayer its own, the mind descends into the heart for the most profound and sacred service of prayer.
All this is accomplished under the guidance of the grace of God. It is harmful to strive for the second before acquiring the first. (On the Prayer of Jesus, p 48)
How long to pray
Be sure to consult your spiritual Father on the amount of time you should devote to the Jesus prayer. As a general rule you should repeat it for a minimum of 15 minutes at any one prayer session. Any less will not help you develop the attention needed for prayer of the heart. You should then fairly quickly work up to a period of thirty minutes. You will need to measure your time to make sure you fulfill your desired time. One way is with a clock. Another way is to use a prayer rope. A prayer rope has 50 or 100 knots typically. Holding it between your thumb and index finger you can index one knot at a time each time you complete one complete recitation of the Jesus prayer.