In my career, I've done more than a few flights over 10 hours, sometimes as long as 14. If you're not in first or business class, sleeping is a challenge. Economy seats only lean back a few inches and even if you manage to fall asleep you'll probably be woken up after a few minutes by someone trying to climb over you, or accidently kicking your seat.
Sometimes it's not even wise to sleep through the whole flight. It's hard to beat the jet lag if you only start adjusting the moment you arrive. You're better off, if possible, to set your watch to the new time zone the day before you head to the airport. Stay awake for their day light hours and sleep during their night hours.
If you have to wake up on one of those long flights, the biggest challenge is overcoming the boredom. I've found several ways that make the time go by just a little faster.
Movies. The airline probably has a selection of movies on their private screens, but most of those movies are either terrible to start with, or have been edited so much they're impossible to follow. If you have a laptop that plays DVD's, bring it with you. Movies that are actually entertaining make a big difference and take care 2 hours of your flight … assuming your battery will last that long.
Reading material. If you're a reader, bring more than one book. It's a shame to a start a book and find out that it's awful when you have nothing else to read. Easy to read thrillers and romances seem to pass time the fastest. If your bring Dostoyevsky, you may be intellectually better off when the plane lands, but it will not have appeared any faster.
If you enjoy magazines, bring four or five. They're quick reads for the most part but also a good form of entertainment.
Puzzles. Sodoku or crosswords are the most popular. This is the flight attendant's weapon of choice in the war on boredom. They're the easiest way to kill the time between meals, books, and movies.
It's an incredible challenge to keep your mind focused on just one thing through the flight. Puzzles are easy to pick up and put down. They provide a smooth transition between the books and the movies. Remember, puzzle books are useless if you can not write in them. Do not forget your pen!
Talk to your neighbor. As long as there's no language barrier, talking to someone who is sharing your boredom is a great time killer. It's a shame to see how few people are willing to chat it up on an airplane these days. Talk to your fellow passengers or flight attendants. Share travel stories or just talk about how bad the movies are.
It'll make the plane ride go faster and you might even make a new friend. Do not be shy, you're all in the same boat … figuratively speaking.
Being prepared before your flight will make your trip a lot smoother. In the hustle of getting to the airport and making sure you're prepared for the trip, people often forget to prepare for the ride.