One technique is the use of repetition... the word "Nevermore" is the only word the bird can say. The narrator even admits that this is probably true when he says, "Doubtless...what it utters is its only stock and store". However, the narrator begins to question the bord, although he knows that the answer will always be "Nevermore". This repetition allows the narrator to sink deeper into his depression by the questions he asks: "Is there balm in Gilead?", and Will I ever "clasp a rare and radiant maiden whom the angels name Lenore?" Deep down, he knows the answer, but he asks the question anyway. Another repetition is the word "Lenore", which is a constant reminder of what he has lost.
Poe also uses rhyme to create a melancholy, depressing mood. Lines 2, 4, 5, and 6 of every stanza end with the "---ore" sound, which is like a moan. The long "o" and the reverberation of the "r" can be carried out to sound like a person in pain, which the narrator is.
The raven is a symbol of death, being a mysterious black bird that arrives at midnight and stays "perched upon a bust of Pallas" just above the man's chamber door. This is a symbol of the lingering thoughts of Lenore's death that the man will never get over.