Begin with Oral Prayer

"For all and everyone it is really useful to begin one's training in prayer by the name of the Lord Jesus by saying the prayer of Jesus orally while enclosing the mind in the words of the prayer. By the enclosure of the mind in the words of the prayer is meant the strictest attention to those words without which prayer is like a body without a soul. Let us leave it to our Lord Himself to transform our attentive oral prayer into mental prayer of the heart and soul. He will do this without fail when He sees us even a little purified, educated, matured, and prepared by the practice of the commandments of the Gospel."
Saint Ignatius Brianchaninov in On the Prayer of Jesus p102

Is the prayer on your lips? Then grace is there as well. But from the lips it must pass into the nous and descend into the heart––and this takes much time and labor. The tongue must toil in order to pay for all its idle talk and its falls, and it must acquire the habit of praying. For without labor and practice, a habit cannot be formed...
Elder Ephriam from Counsels fro the Holy Mountain p 362

It is possible to establish a certain sequence in the development of this prayer. First, it is a verbal matter: we say the prayer with our lips while trying to concentrate our attention on the Name and the words. Next we no longer move our lips but pronounce the Name of Jesus Christ, and what follows in our mind, mentally. In the third stage mind and heart combine in the heart and the prayer is said there. Fourthly the prayer become self propelling....
A gradual ascent is the most trustworthy. The beginner who would embark on the struggle is usually recommended to start with the first step, verbal prayer, until body, tongue, brain and heart assimilate it. The time this takes varies. The more earnest the repentance, the shorter the road.
Archimandrite Sophrony in On Prayer, pp 142-143

You should know that the devil will try to break the unity of the words at all costs and enter into the nous and heart. He will try to make only one small opening in order to put a bomb (a thought) and blow up all this holy effort. However we must not allow him in. We must say the Jesus prayer loudly (vocally) os the the ears will also hear it, because this helps the mind concentrate more...
Metropolitan of Nafpaktos Heirotheos in A Night In The Desert Of The Holy Mountain p 77