"Could you address whether there are suggestions for when to stand, sit, or kneel during prayer? I know this might be heaping too much on for some, but I recall having directions about it many years ago and I don't have that anymore. I might use it sometimes when I am having trouble concentrating or getting too routine and thoughtless in my prayer."
Years ago, I heard a protestant lady complaining about her single experience of going to a Catholic mass: "Stand up, sit down, stand up, sit down,stand up, kneel, stand up! It was like calisthenics or Simon Says!"
I guess no one told her why Catholic worship includes all this moving around. It's so our bodies can help our souls to pray, by becoming a physical sign of whatever prayerful attitude we are trying to cultivate.
There are accepted postures to go along with the Liturgy of the Hours. We are not expected to use them when praying privately. But, as the reader above suggests, they can help us focus on what we are doing. I think I've already posted on this, but it's easier to just write it all up again than to weed through 450-some old posts to do a reprint.
In community, you stand up for the opening, "O God, Come to My Assistance", remain standing for the hymn, sit down for the psalmody, the reading, and the responsory. You stand for the gospel canticle--because it's the gospel after all, and deserves that extra respect, just as it does at mass. Remain standing through the intercessions, Our Father, and conclusion.
That is how morning and evening prayer goes. And night prayer. Daytime prayer: stand at the opening and hymn, sit for everything until the final prayer, at which point you stand thru the finish. Same with Office of Readings.
In reading old Catholic literature, you often see a parish priest depicted as reading his breviary while strolling up and down the garden walk, in the churchyard, or something else along those lines. This is not a rubric, but just an excellent way to keep oneself more awake and attentive if sitting for a long stretch makes one too relaxed and sleepy to pay attention.