Advice for all long-haul air travellers

Be comfortable in your seat
Drink plenty of water
Be sensible about alcohol, as excess leads to dehydration and immobility
Bend and straighten the legs, feet and toes every half-hour while seated
Press the balls of feet down hard on the floor or foot-rest to increase the blood flow in the legs and reduce the chance of clotting in the vessels
Use upper body and breathing exercises to further improve circulation
Take occasional short walks (when in-flight advice suggests this is safe)
At stopovers, where possible, get off the plane and walk about
Avoid taking sleeping pills, which will increase immobility