It is important to reduce the risk of developing a blood clot, especially during travel. The simplest thing would be to exercise your lower leg muscles. The most simplest exercise would be to raise your toes, point your toes towards your head, stretching your calves, and then relax, and then repeat as often as you can remember to do so. If you're in an air travel, getting up for just walking down the aisle would be an important prevention. If you specifically know your risk to be high, you can take additional preventative measures, such as wear compression stockings. You can even take prophylactic blood thinners if you've had blood clots before.
