Over the course of three months, I took 11 flights which had time changes anywhere from one hour to seven hours. I can absolutely attest to the fact that jet lag can make the first day of any trip difficult to enjoy. Eventually, I found a routine that combatted my jet lag, I hope it can be useful to you as well.
This is undoubtedly the most important tip. Drink plenty of water before you leave, on the plane, and when you arrive. People tend to drink less water than normal when they're traveling. This happens for a number of reasons, it may be due to decreased access to water, the cost of water bottles, or even the fear of having to frequent the restroom. Keeping yourself hydrated will be good for your body and your brain during long journeys. Therefore, you should also avoid things that will dehydrate you during the flight, such as alcohol.
MOVE AROUND ON THE PLANE
If you're awake on the flight, you should get up and move periodically. Prolonged periods sitting is unnatural for our bodies.
Don't Sleep when you land
If you flight doesn't land at night, local time, then you should stay awake. A nap won't help your body adjust to the new time zone, so make the most of the day and get moving. Be sure to go to bed at your usual time in the new time zone.
Eat Meals at normal Local times
When I land in a new time zone, I often find that I'm hungry. If it isn't the right time for a meal, I eat something light and force myself to eat breakfast, lunch and dinner at the correct local times.
Use Natural sleep aids
Sleeping pills can be harmful to your body's natural ability to fall asleep, especially when it is already trying to adjust to the change in time zone. If you need something to help you sleep, try melatonin.