For me, one of the most practically helpful aids to meaningful, rich prayer is so Biblical and so simple, it's trickily easy to completely overlook.
"O come, let us worship and bow down;
let us kneel before the Lord, our Maker."
As a human being, I am a body-soul nexus. That is to say, my body & my soul are connected. The posture of my body influences and affects the "posture" of my soul. That's just the way God made us.
Isn't this what Screwtape told Wormwood, when he was giving him advice on undermining and weakening a Christian's prayer?
"At the very least, they can be persuaded that the bodily posture makes no difference to their prayers; for they constantly forget what you must always remember, that they are animals and that whatever their bodies do affects theirs souls. It is funny how mortals always picture us as putting things into their minds; in reality our best work is done by keeping things out."
See if God hasn't made you that way too.
"And he withdrew from them about a stone's throw,
and knelt down and prayed."