What should i do to have a strong lungs?

Exercise,don't smoke: Exercise regularly. Do not smoke, avoid any lung irritants (gasoline, paint, 2nd hand smoke, exhaust, etc.)

Exercise : Try to do aerobic excercise like walking, running, swimming , dancing or cycling for 30 mins a day 5-6 days a week. Stay away from smoking . If possible or interested Yoga and breathing excercise on daily bases is great, but it does require learning or training.