Try to get a book called Taking Charge of your Fertility, the definitive guide to natural birth control and pregnancy achievment by Toni Weschler, MPH. It is very hard to do, but trying to time intercourse for a girl is possible. I have always used the method for birth control, more or less, and when we started a family, I knew exactly what night was best, and we had our first baby, a boy. I was 38 years old at the time, so luckily no fertility problems for me.
With our second child, it took a little longer - we tried about six months or so. We wanted a girl so the idea is to time intercourse a bit before your most fertile day which you can know based on charting, etc. Finally the last month, I no longer cared if we had a girl or not. We just wanted another child and we just used the ovulation kit and had essentially one chance. And what do you know - it was a girl! She is now two. I think because I was over 40, that my cycles were a little harder to predict, and I don't know that an egg is actually released each month. So I wasn't sure if the method was working. Anyway, the book is worth reading and will explain what I am saying so good luck!