The poem is arranged in a total of 5 sentences.  Stanzas 1,2, 4 are each one sentence.  Stanza 3 is comprised of two sentences.  Each sentence is a declarative sentence, with all but the first beginning with the subject of the sentence followed by the verb.  Stanzas 1 and 4 are each compound sentences with the first independent clause being a reference to the woods while the second clause is a reference to an action that the speaker is considering--stopping to watch the woods "filling up with snow" in the first stanza and moving on to keep promises in the fourth.

Poetically speaking, probably the most important device is the repetition of the last line:  "miles to go before I sleep."  As with many of Frost's poems, the first time a line is mentioned, the reader tends to interpret it literally.  The second time, the line becomes more metaphorical and the meaning has broader significance.

Other poetic features to consider are the meter and rhyme.  The poem is structured in iambic tetrameter lines with the rhythm holding true throughout the poem.  The rhyme scheme is an interlocking rhyme scheme with the unrhymed line of each stanza becoming the dominant rhyme of the subsequent stanza.  The closing stanza, of course, ends with a note of finality in that all four lines have the same rhyme.

Other sound devices worth noting are consonance and assonance.  The line that describes the hypnotic appeal of the dark snowy woods repeats  the "s" sound and the long "e" sound:

The only other sound's the sweep

Of easy wind and downy flake

These are a few of the language patterns in the poem.