Here we reach a part of the Mass about which many have written much, usually intensely polemical, about the prayers to be used by the celebrant. Rather than tread through that minefield I will simply say that I don’t see that it really matters whether one use the prayers based on the Jewish berakah prayers that were used by the Church for five or so centuries and in the Ordinary Form today, or the prayers of sacrifice that were used by the Church for fifteen or so centuries and in the Extraordinary Form today. As far as I’m concerned, I think they are equally valuable for different reasons, and it is actually a shame we can’t use them both, but can you imagine how long that would stretch out the offertory? (A private email pointed out to me that I didn’t discuss on which side of the altar the celebrant stands, and I admit I left that out intentionally. It should be clear that I write for those who celebrate eastward, leading the prayers of the assembly, not slipping in behind the altar like a bartender.)
All I want to say specifically about the Offertory is this: pick up Lamburn or Fortescue and follow it as much as you can. The directions are perfectly clear, and I cannot improve on them at all.
I will add a word about the volume of prayers. The tradition for at least fifteen or more centuries (and still, in the Extraordinary Form) has a number of prayers said in what was called the mystic voice, that is, not quite silent, yet audible only to the celebrant and the Almighty. At the time of the deformation, anything that was said this way tended to disappear from protestant rites, as if nothing mattered that the congregation didn’t hear. Now, I am not a fan of the incorrectly labeled ‘silent canon’ but neither do I think that the post-Vatican II notion of bellowing everything in one volume an improvement. I have not come to any conclusions about a good middle way here, and am open to suggestions. Perhaps if everything that used to be in the mystic voice were to be said softly (yet audibly) and everything else in a normal (yet not loud) voice, that would work best. Please let me know what you think.