Ditto to Susan's recommendations to drink water, avoid the pre-packed airline meals and get out of your seat to stretch your legs. Eat fresh and your body will thank you. I also pack my own snacks (you just need to comply with current restrictions against unwrapped foods and opened containers).
Upon arrival at the destination, I try to retire at the time I ordinarily would - just on local time (not home time). For example, although I find it relatively easy to snooze on a trans-oceanic flight, when I get to my final destination, I don't nap. Instead, I'll try to get my body adjusted for the time as immediately as possible by staying up until the time of night I would ordinarily go to bed. This works for me.