Maintain an active lifestyle and exercise regularly -- daily, if possible. Walking, swimming, and bicycling are all great activities.
Manage your weight with exercise as well as by eating a healthy diet.
If you smoke, quit! Nicotine therapy (in patches, gums, or sprays) and support groups can make this much easier to do.
Get your blood pressure checked regularly; take steps to lower it, if necessary.
Report any family or personal history of blood-clotting problems to your doctor.
Discuss alternatives to birth control pills or hormone-replacement therapy with your doctor.
If you are on an airplane for more than 4 hours, either walk or do leg stretches in your seat and also stay well-hydrated and avoid alcohol consumption.