Bring a warm sweater in you hand baggage since the air conditioning system could lower considerably the cabin temperature.
Take the necessary time to effect all the legal flight formalities so to be able to face the journey with the right mental condition.
Avoid demanding activities.
Avoid heavy meals.
Limit alcohol drinks, tea and coffee.
Limit nicotine use.
DURING THE FLIGHT
The safety belt must not be too tight: it could restrain the blood circulation.
Do simple stretching exercises in order to prevent circulation problems, swollen legs ad feet, muscle tensions, back ache, cervical arthrosis, lumbar pain.
Have light meals, eat slowly and limit fizzy drinks, tea and coffee.