Eat a healthy diet. Exercise, even if only moderately. Talk to your doctor about whether you should have the influenza vaccine every fall, the pneumococcal vaccine every five years, bronchodilators, inhaled corticosteroids, or antibiotics for coughs. I have tried to stop smoking and couldn't. You should still stop smoking, but you may need some help doing it.
Many people do.
Ask your doctor to help you find the right smoking cessation program and, if necessary, the right nicotine replacement therapy to help avoid withdrawal symptoms. Many smokers are truly addicted to the nicotine in cigarettes and medication therapy can help them handle withdrawal symptoms.