1. Personification. This is where you give inanimate object human-like characteristics and traits. In the second stanza, Auden describes having airplanes "circle moaning overhead
Scribbling on the sky" about how this person's loved one had died. Airplanes can't moan or scribble; but giving an airplane the ability to do so adds depth to the poem. It makes it feel as if the airplane itself is mourning the death too.
2. Imagery. This is where you use the five senses to convey emotion, and help the reader to feel like they are right there. In the first stanza, there is a lot of imagery that conveys a feeling of grief, sadness and muted emotion. Auden says that we must "stop the dog from barking," "silence the pianos," and bring out a "muffled drum." All of these sensory references indicate sadness. The piano cannot play its joyous music, the dog cannot bark and be happy, and even the drums themselves are muffled and diminished. This enhances the theme of grief.
3. Metaphors. Metaphors compare two different things that have similar traits. In the third stanza, Auden uses metaphors to convey how much the deceased meant to the narrator. The deceased was their North, South, East and West. Here, Auden uses a metaphor to say that the deceased gave the narrator direction, guidance and purpose. Other metaphors: working week, Sunday rest, noon, midnight, talk and song. Each one of those comparisons has different layers that could be discussed, all adding depth and symbolism to the relationship between the narrator and the deceased.
I hope that helps a bit; good luck!