My friend has jet lag. How do I avoid getting it?

Jet lag. Plan on turning your watch to the destination time and behaving like you are at that time as soon as you get on the plane. Avoid alcohol. Once you get at the destination, sleep and stay awake at the times everyone else does at the destination. Use caffeine as needed to stay awake. If it is a big time difference, consider sleeping pills and stimulant medicines.
Try allowing your. Body to at least partially accommodate to the new time before you travel. If heading east, try getting up 30 minutes earlier for several days and going to bed earlier. Melatonin may help. If heading west, reverse the process.