I too find it extremely difficult to sleep on an airplane.
Noise canceling earphones, classical or New Age music, eye mask, comfortable clothes, and a hoodie sweatshirt all help, but what would help the most is not being in those damned uncomfortable Y seats.
One TATL flight I took a particularly strong sleeping pill & was able to get about 5 hours sleep, but normally I'm lucky to get 3 hours. I try to build some extra time into my itinerary to compensate.