Any time you cross more than a couple of time zones, you're likely to get hit by jet lag. One of the remarkable things about the human body is its sense of timing—natural cycles like eating and sleeping are governed by a multitude of changes in body chemistry that tip you off as to when to perform those activities. Unfortunately, yanking your body out of the time zone it's used to can throw that circadian rhythm off. While there's no way to keep jet lag from happening, you can take measures to lessen it's symptoms.
1. Get ready for the Trip by Changing Your Bedtime
This sounds simple, and it is, but it can also help. If you're headed east, gradually move your bedtime earlier over the course of a few days. If you're going west, push your bedtime later by a half-hour or so each night leading up to the trip. This helps your body adjust to the new nighttime you're going to present it with. If you can adjust your mealtimes as well, you'll be even better prepared.
2. Avoid Caffeine, Alcohol, and Other Drugs
Flying is stressful enough without taking away your drug of choice, but you can increase your chances of a smooth transition by avoiding them. Caffeine can keep you up, but it disturbs your sleep once you finally nod off, and alcohol dehydrates you, which can make you feel even worse once the buzz wears off. Stick to water—and plenty of it. Likewise, many people think taking a sleep aid will help them, but unless you're going to be on the plane for the 7 to 8 hours of sleep you're supposed to regularly have, popping a pill will end up leaving you feeling worse for wear once you disembark. The no drugs rule obviously doesn't apply to any important medication you may regularly take. Just be cognizent of the time change if you are supposed to take pills within specified intervals.
3. Sleep on the Plane, If You Can
There are plenty of reasons to go with an overnight flight, not least of which is that it's cheaper to do so. But flying overnight also helps you sleep on the plane, which is a great way to stave off jet lag. Set yourself up for comfort with a blanket, eye mask, neck pillow, and ear plugs. If you can afford a seat with extra leg room, take it. Flying used to be a luxury experience, and while it's fallen a long way from that, squeezing as much comfort as you can out of the ordeal will help you rest along the way—as long as you can afford to do so.
4. Take Care of Yourself
The things you should already be doing for yourself become extra-important when you're putting your body through a time zone change. Stay hydrated! It's one of the most important ways to make sure your body is doing functioning properly. Exercise before you go. It can help you sleep better on the plane. Once you're on the plane, get up and walk around every now and then. You don't want foot swelling or stiffness or any of the other things that come from sitting cramped for too long. Maybe even freshen up on the flight by brushing your teeth or washing your face. Eat sensibly. Some people tout the benefits of a healthy "jet lag diet," but there's no evidence to support it.