Poetic devices are beautiful expressions of speech used by an author/poet to appeal the interest of the reader.
the most common are-
Alliteration- She sells sea shells on the sea shore.
See the sound 'ss' is being repeated....(applies to any sound repeated more than 3 times)
Simile- any sentence in which something is being referred to. He is AS fast as a cheetah.
In this the "he" is being referred to a cheetah.
Most of these sentences use 'As' or 'Like'.