And I could tell What form my dreaming was about to take. (line 16-17)
Just on the basis of his memories of the day, the speaker knows what he will dream about. Strictly speaking, we're pretty sure you can't actually predict your dreams like this. He's making a rhetorical point.
My instep arch not only keeps the ache, It keeps the pressure of a ladder-round. I feel the ladder sway as the boughs bend. (lines 21-23)
The speaker makes a subtle distinction between active and passive forms of memory. A passive form of memory would be the "ache" that reminds him of standing up on the ladder all day. But he also feels the more active, present memory of the ladder pressing into his foot. He truly is reliving the day again.