Noise-cancelling headphones are terrific, and ambien helps too + all the advice above. But if you have one or can afford to get one or borrow one, attach an iPOD or MP3 player with some soothing new age type music of waves at the seashore or birds in the mountains to the headphones if you're going to be sleeping. Then you'll be in your own little world for several hours.

Also, coach bathrooms on long flights often get pretty disgusting after the first few hours of flight. So bring along some extra kleenex in your pocket, some hand cleanser, and avoid drinking more fluid than you need to stay hydrated so as to minimize trips there.