The wrong temperature can keep you awake, so be prepared to adjust if you need to cool off or warm up. Wear layers of clothing or carry a sweater with you. Grab a blanket when you first get on the plane, since there may not be enough available for everyone. In case you get too warm, check the fan when you first sit to make sure it is working properly.
Snag a pillow before takeoff, as well. Consider bringing your own pillow in your carry-on if you need something more comfortable, such as a bone pillow to support your neck. Take your shoes off and prop up your feet; it is easier to sleep with your feet raised. If light bothers you, wear a mask or eye shades.
If you can, choose a window seat so you have something to lean against and less chance of being disturbed by neighbors. Seats in the middle of the plane are the most stable, so try to sit over the wing or as close to it as possible.
Tell the people next to you that you need to sleep. If they stay awake, they can help prevent other passengers or the flight attendants from waking you, and they are likely to be less disruptive themselves.
Carry headphones or ear plugs. Noise-blocking headphones can prevent engine drone and ambient noises from disturbing you. Listening to music from a CD player of mp3 player may also help you relax and drown out other sounds.
Anti-airsickness medications often cause drowsiness, so taking a dose before traveling can help you sleep. Older antihistamines typically have the same effect. You can also take melatonin to help you get to sleep and to lessen jet lag.
