Sleep (naps when possible)
No alcohol
Hydrate with warm liquids (water and tea regularly)
Hand sanitizer
Vitamin D
Watch diet carefully and don't just consume foods because they are put in front of you
Yogurt
Regular moderate exercise

I'm not sure how old you are, but interestingly, I was a very frequent traveler in my late 20's (LHR to HKG was a frequent route) and early 30s. Surprisingly, as I've gotten older, although the body definitely experiences the issues of aging, for some reason travel, particularly long haul trips, which I have to do in Y, is tolerated better.