To enter into sleep we must left consciousness behind us and walk deeper into our body and out of our body in a rythmic way....
We must then relax to be permeated by the natural rythm of our body, respiration,in and out , in and out ...
To relax deeply we must use a "music" more like a repetitive mantra mimicking our slow respiration rythm...
The most useful music will also act on the soul not only on our body, and must directly pacify our feeling soul... This "music" for better working must not induce a new cycle of emotional reaction ( like conventional classical music or worst pop music ) but instead must make impossible or impede any feeling except absolute peace...
I suggest this music done by a trained recognized sound healer : Jonathan Goldman : Celestial harmony ...
https://www.youtube.com/watch?v=aJRpoUk-mpU&list=RDaJRpoUk-mpU&start_radio=1
but Hildeard of Bingen music, Indian mantras or Gregorian singing will do well ...