It's random what gender the baby will turn out to be, just try untill you get one, hey I recommend having a girl and a boy.
Having babies is not like ordering a box of assorted candy, where you choose which one you want. If you're asking this question, then I assume you are probably not in a stable relationship, where you make love to have a baby because you both want to be parents; and make a long life relationship together.
Depth of penetration has a significant effect on the sex of the baby. Deep rear penetration (doggy style) is more likely to favour a boy; shallow penetration in the missionary position is more likely to favour a girl. --- And there is nothing wrong with sex selection - my aunt had to have five girls and endless miscarriages in the days before contraception, before her husband got the boy he wanted.