Origen the Liturgist

Origen's treatise On Prayer has an interesting section at the end about the formalities of prayer which give an interesting insight into 3rd century practices.
On standing and praying

Of all the innumerable dispositions of the body that, accompanied by outstretching of the hands and upraising of the eyes, standing is preferred—inasmuch as one thereby wears in the body also the image of the devotional characteristics that become the soul. I say that these things ought to be observed by preference except in any special circumstances, for in special circumstances, by reason of some serious foot disease one may upon occasion quite properly pray sitting, or by reason of fevers or similar illnesses, lying, and indeed owing to circumstances, if, let us say, we are on a voyage or if our business does not permit us to retire to pay our debt of prayer, we may pray without any outward sign of doing so.

But kneeling has its place as well

Moreover, one must know that kneeling is necessary when he is about to arraign his personal sins against God with supplication for their healing and forgiveness, because it is a symbol of submission and subjection. For Paul says; For this cause I bow my knees unto the Father from whom is all fatherhood named in heaven and on earth. It may be termed spiritual kneeling, because of the submission and self-humiliation of every being to God in the name of Jesus, that the apostle appears to indicate in the words: that in the name of Jesus every knee should bow in heaven and on earth and under the earth.
It should not be supposed that beings in heaven have bodies so fashioned as actually to possess knees, since their bodies have been described possibly as spherical in form by those who have discussed these matters more minutely. He who refuses to admit this will also, unless he outrages reason, admit the uses of each of the members in order that nothing fashioned for them by God may be in vain. One falls into error on either hand, whether he shall assert that bodily members have been brought into being by God for them in vain and not for their proper work, or shall say that the internal organs, the intestine included, perform their proper uses even in heavenly beings. Exceedingly foolish will it be to think that it is only their surface, as with statues, that is human in form and nothing further underneath.

A very literal ad orientem

A few words may now be added in reference to the direction in which one ought to look in prayer. Of the four directions, the North, South, East, and West, who would not at once admit that the East clearly indicates the duty of praying with the face turned towards it with the symbolic suggestion that the soul is looking upon the dawn of the true light?
Should anyone, however, prefer to direct his intercessions according to the aperture of the house, whichever way the doors of the house may face, saying that the sight of heaven appeals to one with a certain attraction greater than the view of the wall, and the eastward part of the house having no opening, we may say to him that since it is by human arrangement that houses are open in this or that direction but by nature that the East is preferred to all the other directions, the natural is to be set before the artificial. Besides, on that view why should one who wished to pray when in the open country pray to the East in preference to the West? If, in the one case it is reasonable to prefer the East, why should the same not be done in every case? Enough on that subject.