1. Don't smoke, and avoid second-hand smoke. It's by far the biggest risk factor for developing lung cancer. While the proportion of Americans who smoke has dropped almost in half¡ªfrom 42 percent to 23 percent -- since 1965, 46.5 million still smoke. Tobacco use also increases the risk of mouth, tongue, throat and bladder cancers and accounts for 30 percent of cancer deaths a year.

If you smoke, ask your doctor for help quitting and urge family members who smoke to do the same. ¡°Today there are more ways than ever before to help smokers quit,¡± says Michael Thun, M.D., head of epidemiology research at the American Cancer Society in Atlanta. ¡°Among them the drug Zyban and nicotine gum, patches and nasal spray.¡± And if you don¡¯t smoke, avoid being in the presence of those who do. Second-hand smoke, or environmental tobacco smoke, also raises your risk of lung cancer. It causes 3,000 lung cancer deaths annually in nonsmokers, according to the ACS.

2. Control your weight. Health-conscious Americans know that being overweight boosts their risk of heart disease, high blood pressure, stroke, diabetes and arthritis. But many people don¡¯t realize that developing cancer is also linked to extra pounds. According to Dr. Thun, some of the cancers linked to excess weight include breast, uterine (endometrial), ovarian, colon, rectal, esophageal, kidney, gall bladder, liver, pancreatic, stomach and prostate, as well as the blood cancers leukemia, lymphoma and multiple myeloma.

Since 1982 American Cancer Society researchers have tracked the weight and cancer risk of 900,000 American adults. Their findings show that compared with people who maintained their recommended weight, those who were obese -- as defined by having a body mass index of 40 or higher -- were 57 percent more likely to die from cancer. ¡°About 90,000 cancer deaths annually are associated with obesity,¡± says Peter Greenwald, M.D., director of cancer prevention for the National Cancer Institute in Bethesda,Maryland.

3. Get physical. Exercise specifically reduces the risk of breast, colon and rectal cancer. It's not clear why exercise decreases breast cancer risk, which strikes 211,000 women a year and kills 40,000, but one reason may be that physical activity lowers the number of fat cells, which reduces levels of cancer-stimulating estrogen. "Colon and rectal cancers take a similarly huge health toll, with 150,000 new cases and 57,000 deaths a year," says Dr. Thun. It¡¯s also not exactly clear why exercise lowers the risk of colon and rectal cancers, but one theory is that it reduces constipation, which decreases the time carcinogens in stool are in contact with colon and rectal tissue.

"To get enough exercise to reduce your cancer risk, you don't have to join a gym," says Dr. Greenwald. "Just be more physically active every day. The intensity of exercise is not as important as its regularity. A brisk half-hour walk every day is enough."

4. Drink less alcohol. Having more than two alcoholic drinks a day for men, and one for women, increases the risk of many cancers including mouth, throat, larynx, esophageal, liver and breast. (One drink is defined as one 12-ounce beer, a cocktail containing 1.5 ounces of 80-proof liquor, or 5 ounces of wine, a standard wine glass about half full.)

However, modest alcohol consumption -- up to two drinks a day for men and one drink a day for women -- may reduce the risk of heart disease. ¡°If you¡¯re at high risk for breast cancer, you shouldn¡¯t drink,¡± says Dr. Thun. ¡°However, if you¡¯re at low risk for breast cancer but at significant risk for heart disease, then a little alcohol may be beneficial. Your doctor can help you decide based on your health situation.¡±

5. Take a daily multivitamin and mineral. Vitamins do not offer magical protection against cancer. They are not a substitute for a healthy diet of fruits and vegetables, and they don¡¯t eliminate the damage caused by a diet low in plant foods and high in saturated fats. ¡°A multivitamin is an easy way to get some cancer-fighting antioxidant nutrients,¡± says Sally Scroggs, R.D., senior health education coordinator of the Cancer Prevention Center at M.D. Anderson Cancer Center in Houston. Just don¡¯t overdose. Very high doses of many vitamins and minerals can cause problems. For example, vitamin B6 can cause nerve damage, and large doses of vitamin C and magnesium can cause diarrhea; worse, megadoses of vitamin D can be toxic. To be safe, stick to a multivitamin and follow the label instructions. In addition, if you smoke, steer clear of beta-carotene, a form of vitamin A, because it has been linked to an increased risk of lung cancer in smokers. Look for a multivitamin/mineral that contains selenium, an antioxidant mineral associated with a reduced risk of some cancers.