Prepare your trip down to the last sock, and have everything ready to go a day or two before departure. If you scramble for your passport while the taxi is waiting and rush to the boarding gate breathless, you'll be stressed, which isn't conducive to the rest you need.
Drink water, not alcohol. Flying is very dehydrating, so you need water or juice to keep the symptoms of jet lag from being even worse. Alcohol further dehydrates you. Magellan's recommends that you drink 8 to 16 oz. of water for every hour you're in the air.
Wear clothes and shoes that are comfortable enough to sleep in.
Avoid sleeping pills. If there is an emergency, you will need to be alert, and sleeping pills often have lingering effects, making normal jet lag even worse.
Set your watch to the time it is in the country where you're going, and don't constantly do the math to figure out what time it is back home. Once you're on the plane, be in the European mindset.
Sleep as much as possible while you're on the plane. Many flights to Europe from the U.S. are overnight flights, so if you can manage five or six hours, when you get to London or Paris early the next morning you'll be ready to start the new day.
Take your bags to the hotel once you've landed, leave them and take a walk. Exercise, fresh air and sunshine will help tell your body that it is daytime and it should be awake. If you must take a nap during your first day in Europe, make it a short one, no more than two hours.
Go to bed early--European time--on your first night there. Hopefully your first day in Europe will have been so exciting that you sleep soundly through the night.
