If you smoke, stop. It will immediately cut your chances of a heart attack by a third.
Get exercise and eat right. The American Heart Association recommends 30 minutes of moderate exercise a day, 5 days a week. Eat plenty of fruits, veggies, and whole grains to keep your arteries healthy.
For some people, taking a daily aspirin will help. Talk to your doctor to see if it's right for you.
Also, find positive ways to manage your stress.