Tips for having a comfortable sleep on your next flight

Sleeping in one of these is like sleeping in a straitjacket, especially if the seat next to you is unoccupied, or worse, the entire row is empty (as happened to me on a flight from Australia—14 hours in the air, an empty row, and the worst flight I’ve ever had). What could have been a nice sleep nook is now more like, well, an airplane seat.