Interesting discussion...
I was raised secular humanist, so I never prayed as a child, a youth or a young adult. I said my first prayers when I was already in my 40-s, in a Presbyterian Church. They were very "Protestant" - entirely in my mind, absolutely spontaneous.
Just recently, when I became a catechumen, I learned to pray aloud (not "loudly," actually whispering or saying words of prayers in a very quiet, soft voice - but not merely in my head), and in front of the Holy Icons. It is an entirely new and different and very blissful experience to me. I, indeed, say those prayers that are written in my Ukrainian Orthodox prayer book, word to word, without any improvisation. These are the prayer to the Holy Spirit ("Heavenly King, Comforter, the Spirit of the Truth, Though Who abidest everywhere and fillest everything..."), the Trisagion, the Small Doxology, the Lord's Prayer, and the prayer to the Most Holy Theotokos ("Theotokos the Virgin, rejoice, blessed Mary, the Lord is with thee, blessed thou art among women...). I do really feel that the words of these prayers are "THE" words that need to be said. What can I, in fact, "add" to the sentence, directed to the Most Holy Theotokos, "carry our prayers to thy Son and our God, so that He saves our souls for thy sake!"? What exactly are these "our prayers," I am sure the Lord knows, He hears them even before "we" say them or rationally-cerebrally "formulate" them in our thoughts...
Yet, I do also say short "personal" prayers - simply mentioning names of my relatives and close friends, and imagining them as I ask the Lord to save them, to have mercy on them, to protect them or, if they have died, to rest their souls and to create for them memory eternal.
Again, I am probably different from most people on this list, or maybe even from all, because you guys were raised Christians (or non-Christians but still religious), and are used to prayer from early childhood. So, my experience is probably of little use, but I just felt like sharing.
George