Jet lag occurs when rapid travel across multiple time zones disrupts your internal body clock. Circadian rhythms, in harmony with night and day, control your sleep-wake cycle. Your symptoms may be more severe with the more time zones you cross.
Traveling east makes it harder to adjust to new time zones than traveling west. If you are traveling east, try melatonin at bedtime to get to sleep earlier and drink caffeine in the morning to help you wake up until you feel adjusted to the time zone.
Before traveling, try to get plenty of sleep for several days leading up to your travel. It is good to avoid alcohol on the flight. Once you arrive, get as much exposure to daylight as possible. You might also consider doing some extra exercise.
American Academy of Sleep Medicine (sleepeducation.org)