The Independent Air Traveler and eHow have compiled useful tips for sleeping on planes.

Choose the right airplane seat
Avoid completely the last row in the plane, and any seats just in front of the exit row. Think twice about bulkhead, exit row, and aisle seats. Window seats give you a wall to lean on, and your neighbor won't need to disturb you on the way to the lavatory.

Exercise, Try to get tired
Make sure that your body will be tired for the flight: Before your departure, avoid sleeping in, napping and try to get some exercise. Skip the temptation to have a cup of coffee before boarding, and even more so when the coffee cart comes around.

Inflight meals help you fall asleep
Ask what time the in-flight meal will be served. Falling asleep is easier on a full stomach. Tell your neighbor that you plan to sleep. The purpose is twofold: He'll leave you alone, and he can discourage the flight attendants from disturbing you while you sleep.

Another nice tip to avoid noise: Seats positioned in front of the engines are far quieter than those behind the engines.

Source: The Independent Traveler | eHow | Gridskipper