I put them over my socks as it bad enough not being able to find my shoes on a long flight without having to search around for my socks as well. Flight socks also stop you getting wet feet whenever use use the facilities on a plane.
What I also do is start taking low dose aspirin a few days before the flight and continue until I arrive back home as I find it helps circulation and I seem able to cope with the heat easier. Make your own decision on that.![]()