How to comfortably sleep on airplanes

I think there are probably three keys:
1, Proper preparation
2, Good seating
3, Contingency handling

1, Proper Preparation:

What are the keys to rest? Comfort, bodily preparedness, space, lack of distractions, temperature, among other things.

Comfort: neck pillows are lifesavers. They make sleeping on your back much easier. I particularly like neck pillows wi…