I was really good at smoking for a long time. The key for me was when I asked myself if I was going to smoke the rest of my life. If the answer was no, what was I waiting for exactly? it was time to htfu and take care of it! Cold turkey. I sucked on cinnamon sticks for a while.

Of course your lung capacity will get better. That's a no brainer. You're probably starting to ride harder, that will wind you whether you smoke or not.

One more thing, you may put on weight. Don't sweat that until you take care of the smoking thing. Once you can start to tackle the weight, you'll have biking to help. You can do this but you gotta have your game face on.