Best Answer - Chosen by Voters
First of all, know that this isn't an exact science, and there is no guarantee that this works- its just stuff I've read on the internet - go onto google and search for sex determination.
Timing of intercourse can have a lot to do with which sex baby is created! One theory is that sperm that carry the male chromosome are tiny and fragile but very quick, where as the female sperm are larger and stronger, but rather sluggish. Those that adhere to this theory claim that you can improve your chances of conceiving a boy, for example, by timing intercourse one single time as close to ovulation as possible, then not again during the same cycle. The reasoning behind this being that the male sperm would race to their reward much faster than the female sperm. If you want to try for a girl using this same theory, have sex 2-3 days before ovulation (and not again during the same cycle), as this ensures that all the make sperms die before the egg is released leaving only female sperms to fertilise the egg.
I hope that info helped. Have fun, and best wishes.