I know the theory about doing the deed before ovulation but that didn't work for us.
I remeber reading or hearing something about changing your diet to alter the acid/alkaline environment of your fango to make the female sperm survive longer/male sperm die but I can't remeber what the changes need to be....
BTW, Girl OR Boy would be cool, our youngest is such a lovely little boy that to make another one like him wouldn't be sooo bad