The three keys to overcoming jet lag are prevention, adjusting your cycle, and natural light.

Prevention

Overcoming jet lag begins three days before you fly. For these three days, eat more protein that usual for your morning meal, and more carbohydrates than usual for your evening meal. You might be compromising your diet a little, but the trade-off is well worth the reduced or eliminated jet lag at the other end of your journey. The protein / carbohydrates eating pattern essentially conditions your body to expect proteins early in the day and carbohydrates late. When you get off the airplane at your destination, continue this eating pattern for at least three more days. You'll be helping your internal clock recognize the new time zone and adjust to it.

Adjusting Your Cycle

Most airlines make the big mistake of feeding you on the plane (assuming they still do feed you on the plane) according to the schedule of the place you just left. This is exactly the wrong thing to do. Instead, as soon as you get on the airplane, start adjusting your cycle to the time of day at your journey's end. This means you should set your watch to the new time zone, and as much as possible you should try to eat and sleep according to this new time of day. Some airlines let you buy food and drink on your own schedule, which makes this adjustment somewhat easier to accomplish. If your airline insists on serving you breakfast when your new time zone calls for dinner, just do the best you can by eating selectively, eating appropriate food you brought onboard with you, or holding onto your meal until it's "time to eat" at your destination. It's also important to try sleeping, or at least closing your eyes and resting, when it's "night time" at your destination.

Natural Light

After you arrive at your destination, absorb plenty of natural light. For at least three days you should sleep with the shades up so the sunlight will awaken you, sit near windows whenever possible, and refrain from wearing sunglasses. The sunlight helps your inner clock recognize what time of day it is, and adjust itself, and your body, to the new time zone.

Some people just have a harder time than others adjusting to large time zone changes, and your ability to adjust also changes with age as well as with your overall health. But whatever time zone adjustment capabilities you bring to the table, the simple regimen outlined here will help you adjust with less discomfort and mental fuzziness, and with fewer other symptoms than you'd experience if you go "cold turkey" without it.