Medically speaking, jet lag is practically unavoidable, especially if travel consists of passing through several time zones. The body’s internal clock has a hard time adjusting to drastic changes in time zone, and this can lead to anxiety, sleep deprivation, insomnia, nausea, and more. I won’t get into the science behind it (because I have no clue; Let me refer you to Google), but it involves Earth and time and humans and some other things.
Unfortunately, jet lag is just a part of long-distance travel (when going from East to West and vice versa). That being said, there are still ways to reduce the intensity of jet lag and avoid the misery that sometimes may seem sure to ensue.
Try to adjust to local times immediately. Your body won’t want to let that happen, but try your best as it will speed up the recovery process. If you land late at night, try to go to bed. If you land early in the morning, eat some breakfast and try to spend the whole day up and about (good luck). A quick nap isn’t a bad idea, either. Just be sure not to sleep all day. Immediately adjust your schedule to the new time zone too. Eat lunch at lunch time, go out in the evening, and so on and so forth.
The general rule of thumb is that the recovery process takes about one day for every one or two time zones crossed. Well to hell with rules, and to hell with thumbs. With a strong enough body and an even stronger mind, you can adjust to the new time zone quickly, and jet lag will be a thing of the past.