Normally our body is able to adjust our biorhythms only by 1 hour every day. To make the transition easier, you can start preparing for the new timezone in advance by shifting your daily routine closer to the destination time. Let’s say you’re flying eastward to country with +3 hour time difference (your current 7am is their 10am). You can start adjusting 2 days before you leave by going to bed and waking up 1 hour later each day, getting closer to destination time even before you travel.
If you’re crossing too many timezones this may not be practical, but each hour of adjustment counts. Adjust as much as your daily schedule allows you, and you will catch up with the rest of difference during your flight and first day or two after arrival.