Get the Timing Right
According to the Shettles method, the timing of conception is the biggest factor in determining the sex of your baby. Along with some other medical experts, Shettles claims that Y-chromosome sperm (boys) are faster swimmers than X-chromosome sperm (girls). However, girl sperm are thought to be more "resilient," surviving longer in the reproductive tract than boy sperm.
Based on this theory, you're more likely to conceive a girl if you have intercourse every day for two to four days before ovulating and then abstain from sex one to two days before ovulation and a few more days after ovulation. The premise is that by the time you ovulate, all of the male sperm have died off leaving only female sperm to fertilize the egg. Conversely, if you have intercourse on the day you ovulate, the faster-swimming male sperm may beat the girls to the egg. This approach means you'll have to know your cycle. and do some very careful calendar watching, or take an ovulation test to determine precisely when you're ovulating.