(1) Business Class!
Treat yourself well on 10hr + flights. Can't leave home without it.

(2) Stop overs of at least 2 hours (no less, no more).
Incheon Airport -- just as an example -- provides dreamy shower rooms for any class. Most Biz Class lounges do as well.

(3) Don't be a glutton and eat too much on a plane. You'll just end up with a tight, full, bloated feeling. Most uncomfortable. The very thought of eating three big meals within 10+ hours makes me gag.

(4) People-watching in airports. Flyers are in general a pretty weird group. I love watching nerds look they've been caught, like a deer on the road, wide-eyed and always just on the verge of freaking out.
Always priceless.