When to conceive based on gender
It's mostly just luck of the draw which gender your baby will end up being. However, I have heard (and it ended up being true for us) that boy sperm swim faster, and girl sperm live longer. If you buy into that theory, it would make sense that to have a girl, you need to be having sex just before, or right at the start of ovulation, and to have a boy, you need to plan to have sex towards the end of ovulation.
Please remember this "expert advice" is completely based on a superstition and old wives' tale.... though like I said, it was true for all three of ours ;)
What other ways have you heard of trying to be sure you have a specific gender child?