1. Alliteration is the repetition of a consonant at the beginning of adjacent words, or words that are located near each other. It can be seen at the very beginning of the poem, in the Line 5 - "my most immemorial". In this example, it is mixed with consonance (as the Ms are repeated inside the word "immemorial" as well as at the beginnings of the three words), conveying the meaning of intimacy and excitement. A pure alliteration can be seen in the Line 103 - "sinfully scintillant". It creates a hallucinatory effect.
2. Assonance is the repetition of the same or similar vowels in adjacent words or words located near each other. There are numerous examples of assonance in this poem. In Line 3, we see the alteration of /i/, /ɪ/, and /ɛ/ "The leaves they were withering and sere". It creates a wailing sound, conveying the meaning of sadness because the speaker's beloved is dead. Also, the Line 7 is full of of /i/ and /ɪ/: "In the misty mid region of Weir".
3. Consonance is the repetition of similar or identical consonants in nearby words, but those consonants don't necessarily have to be at the beginning of the words. We have it at the beginning of the poem in line two - "crispèd and sere" (the repetition of S and R), which sounds onomatopoeic, so that we can almost hear the sound of dry leaves.
4. Imagery is the use of language in a visually expressive and evocative way. The poem is replete with examples of imagery. The "ashen and sober" sky, the "crispèd and sere" and withering leaves, the "dim lake of Auber", the "misty mid region of Weir" - all those images set the bleak, grim and uncanny mood in the poem, preparing the reader for the encounter with the tomb of the speaker's beloved.