There are several poetic devices in the poem. I'll give you a few examples to help you get started on finding more.
One device Frost uses is rhyme. Look at the first four lines. Line 1 ends with "tree," line 2 with "still," line 3 with "fill," and line 4 with "three." This makes and ABBA rhyme scheme. Line 5 ends with a new sound, "bough," so we assign a new letter, C, to that line. See if you can figure out the rhyme scheme for the entire poem.
Another device he uses is imagery, which is the mental pictures evoked by the poem. I imagine a chilly late-fall afternoon when I read the poem. What images does it evoke in you?
Another device is alliteration, which is the repetition of sounds. Around the middle of the poem, Frost keeps repeating the "s" sound:
Stem end and blossom end,
And every fleck of russet showing clear.
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.
Toward the end of the poem, Frost uses personification: "Were he not gone,/ The woodchuck could say whether it's like his/ Long sleep, as I describe its coming on,/ Or just some human sleep."
According to the Masterplots commentary, the entire poem is an extended metaphor "in which the activity of harvesting apples represents other kinds of activity."