First of all, how old are you? Why dont you just get married before having a baby?
But anyways, yes.. You can take folic acid supplements to help ya. Also, having sex with man on top or from behind will increase your chances, and putting a pillow under your butt after sex and sitting there for a while after will help. If at all possible lol, if you orgasm after he 'goes' in you, it helps.
Im not sure if your bf's smoking affects anything, but he should stop anyway, its not a very mature thing to do especially if youre about to start a family!
<3
gaby