its great that you want to have everything set and be prepared as best as you can be before having a child.
some things you can start doing, is if your not already taking a multi-vitamin start taking one to keep you healthy, go to the gym or exercise at home to stay active, again healthy, eat healthy, you could talk to your doctor about this and see if he or she has any more suggestions too. you seem to be doing all the right things, quitting smoking is such a good thing to do too, good for you!
talk to your doctor, to see if they have suggestions on what else you could be doing to help prepare your body for a pregnancy.
i have a 5 month old and im 19, my pregnancy was not planned, but a helpful tip my doctor gave me was, this is no time to start a diet but to make sure you eat the right amount of foods, drink plenty of water, walk aroud, but take it easy.
i took a vitamin called Materna, its good to take this before getting pregnant and during pregnancy too, to make sure the baby gets the right vitamins and minerals.