The simple answer is: you can't. For an average couple, it is very difficult to influence the gender of their baby. Although a 2008 study suggested that women who ate cereal for breakfast every day during conception were more likely to have boys, some scientists questioned the study's analysis and results.
Some people believe that the sexual position during conception can influence the baby's gender, but this theory has not been proven. Other studies suggest that the timing of intercourse affects the baby's gender—for example, having sex a few days before ovulation increases the likelihood of having a boy, while having sex close to ovulation increases the likelihood of having a girl. In reality, this is also unreliable.
In very specific cases, such as when a couple knows they may pass on certain genetic diseases to a specific gender (usually boys), they may use high-tech methods to increase the chances of having a girl. These methods include:
Although these techniques are feasible, few couples choose the baby's gender solely for personal preference.