Have sexual intercourse regularly between 5 days before ovulation and 5 days after. You can use a period tracker app to see when your likely ovulation date is, or if your period is always regular, then it’s 14 days before your next period. I also strongly recommend stopping the smoking (both you and your husband, and anyone else in the house) plus taking folic acid every day:)
https://sg.theasianparent.com/ways-organically-improve-fertility