There is actually a lot of info about this on the internet. It says you can start taking the low dose Aspirin 2-3 days before the flight and you will cut your chances of getting a traveler's clot by a third. You can also wear compression stockings and drink lots of water. I wouldn't stress out about it, but know the symptoms of a clot because it could come a few days after the flight and the bad part would be if it went to your lung. You would want treatment asap. I'm sure that you will be fine, but it's good to be prepared.