No resources needed, you just have to keep at it:

  * lay down
  * set a 20 minutes timer
  * close your eyes and try to relax, don't open them until the timer rings, even if you are not sleeping
  * repeat daily, ideally around the same time every day

Took me a week but now I sleep almost instantly

If you have troubles getting up afterwards, try a powernap: drinking one cup of coffee right before napping. The caffeine will kick in at about the same time your nap ends.