Quit smoking and you help eliminate the single most preventable cause of premature death and illness in the United States today. If you succeed, you will join the ranks of 34 million Americans who have sworn off cigarettes in the past 20 years.

Chances are, however, you will also share Mark Twain's experience. "To cease smoking is the easiest thing I ever did," Twain said. "I ought to know because I've done it a thousand times."

But even if you fail at first, take heart: The Office of Smoking and Health, part of the U.S. Health and Human Services Department, reports that smokers who have tried to quit at least several times are generally the ones who finally succeed.

Quitting techniques range from going "cold turkey" to taking sophisticated smoking cessation courses. Whatever method you choose, psychologist Neil Grunberg and his assistant Deborah Bowen have outlined a series of strategies for easing the stress in a special issue of the Journal of Cardiac Rehabilitation set for publication early next year. Among their best bets for quitters:

* Motivation. Believe that you are at risk for health problems due to smoking, and you'll be more likely to quite successfully than someone who stops for other reasons.

* Preparation. Realize that you may experience a variety of withdrawal symptoms. Recent ex-smokers often report feeling irritable, anxious and emotional and say they have difficulty concentrating. Behavioral effects may include worsened muscular coordination and slight memory changes. Physically, ex-smokers may experience nausea, sleep disturbances, headache, gastrointestinal problems, body weight gain and changes in brain wave activity that suggest a shortened attention span. There are also heightened adrenaline levels in the body -- a biochemical indicator of stress.

While none of these symptoms last more than a week or two, failure to recognize them as a normal part of cigarette withdrawal can lead to increased anxiety and fear in patients who think they are generally "falling apart" mentally or physically.

* Lists. Identify the situations where you will be most tempted to smoke again, think of ways to avoid those high-risk situations and write them down. Carry the list with you and read it often. Awareness "usually helps the the ex-smoker avoid relapse."

* Social support. Enlist the help of family, friends and colleagues. "It's important to prepare them to deal with irritability and other changes on your part."

* Exercise. Maintain the same level of physical activity you had when you were smoking. Studies show that animals become lethargic and much less active during nicotine withdrawal, which could also help account for body weight changes.

* Attitude. Think of yourself as an ex-smoker rather than a smoker who is trying to quit. Remember that you, not the cigarettes, are in control.