When I ran track my chest got bigger by two inches just because my lungs expanded. I knew because I didn't gain any weight. Also playing the didjeridoo has increased my lung capacity, and singing on stage with no mike. My lungs probably have almost twice the capacity as my smoking buddy.

Definitely quit cigarettes. Try and take more frequent, but smaller hits. I used to take huge hits because I thought I had to. Now, I may inhale some smoke, then finish the inhale with fresh air, to push the smoke down into my lungs. I get just as high, and it's not as harsh.

You can also bake, make Green Dragon or hash oil, or vaporize if you don't want to smoke.

Poor posture is also bad for your lungs, and all your organs because it squishes them. Sitting up straight and breathing deep should help.

Try this breathing exercise. Breathe in slowly, til your lungs are completely full, then hold it in, then inhale a little bit more (you will be able to) and still hold it in. Exhale slowly. This should help you slowly increase your lung capacity.