a spiritual guide is recommended
It strongly very is, in Eastern Orthodoxy as in buddhism. They say there is something that just can't be transmitted through a book.
Translations of some of this material is online, with some links at fruitofthecontemplativelife.org under charsimatic christianity.
I believe we still haven't found the full original instruction though. No rush.
GregKavarnos, you have a copy?
My mother does this practice. I even made her a "mala" for her practice.
The prayer at the top of the wiki article is correct and is the short version:
"Κύριε Ἰησοῦ Χριστέ, Υἱὲ τοῦ Θεοῦ, ἐλέησόν με τὸν ἁμαρτωλόν."
The full version is:
"Κύριε Ιησού Χριστέ ελέησόν με τον αμαρτωλόν, Υπεραγία Θεοτόκε Σώσον ημάς, Άγιοι του Θεού πρεσβεύσατε υπέρ υμών."
Lord Jesus Christ, Son of God, have mercy on me, the sinner, Holiest Mother of God Save us, God's Saints intecede on our behalf.
Transliteration: ki-ri-e i-i-soo hris-te e-le-is-on me ton a-mar-to-lon, i-per-a-gi-a the-o-to-ke so-son i-mas, a-gi-i too the-oo pres-vev-sa-te i-per i-mon
Now, as for the breathing. I must say I don't really know, but, the "stance" used would definitely effect the breathing. The practitioner sits on a chair, "slumped" forward resting their elbows on their thighs and gazing at their navel.
But again, these are instructions that are best received from a spiritual teacher (πνευματικό) as they will will give you necessary details for your practice.