Before You Go
Treat your body well before you fly. Exercise, sleep well, stay hydrated and stay sober. The worst thing you can do is get on a long-haul flight with a hangover.
Some travelers like to exercise before they go to the airport. (This can actually help you sleep better on the plane.) Once you're at the airport, avoid the escalators and moving sidewalks. Instead, walk and take the stairs on the way to your check-in area and gate connections.
Adjust your habits before you leave. If you are traveling from the East to the West Coast, you're facing a three-hour time change and you should try to adjust your internal clock. Three or four days before you leave, start to stay up a little later than usual, and sleep in a little longer. That way, if you become accustomed to falling asleep at 1 a.m. and waking up at 9 a.m. on the East Coast, it will be the same as falling asleep at 10 p.m. and waking up at 6 a.m. on the West Coast. Traveling west to east, do the opposite: get up and go to bed earlier.
Wearing two watches, one set to the current time, and one to the time at your destination, can help you prepare yourself mentally for the coming time change. Many business travelers also use this tactic to stay in touch with what's happening back at the office.