I have suffered from this in the past and there are some precautions you need to take.
Don't sit for too long in one spot. If you are working get up and have a walk around every half hour or so. It is just to make sure everything is circulating properly.
Drink lots of water and exercise regularly. There are no tricks that one needs to do but just be aware of the problem. Being hydrated is a key factor.
When travelling on an aeroplane make sure you drink more fluids as in the plane you dehydrate a lot quicker than normal. The air is dryer and you need to stand up and stretch the legs.
Other than that there is very little once can do.
Walk, walk, walk.
There are other ways of course, but simply walking regularly, and staying active, is cardiovascular exercise, and it's good for the circulation.
Sometimes, it's a real pain having to walk and bike everywhere, but my health is above average for my age range, so I'm grateful for that aspect of my life.
If walking is not an option, you should figure out something to get your blood pumping above resting rate, on a regular basis.