First, I try to be tired.
I find it easier to sleep undisturbed in a window seat though I generally prefer aisle.
Loose, comfortable clothing.
Eat before getting on the plane.
Noise-cancelling in-ear headphones,
A sound track of some sort that masks external noises I might focus on. Typically, I prefer a lot of talk, so long podcasts, talk-heavy movie soundtracks, lectures, even stand-up comedy. Basically, anything with a reasonably consistent voice and volume. Set to loop eternally (because otherwise I wake up when it stops).
I don't drink or use sleeping pills.
wg