Here are the three things you need and the easiest, cheapest, best way to get them (in my own opinion. Please keep in mind I'm not an expert or medical professional and I can not make guarantees -if you have any questions please read the affiliate disclosures and terms of service), but this is what worked for me):
1. Step One: Know Your EXACT PH Going In. This is very important. You'll need a highly acidic PH to conceive a girl, so it's important to know where you are so you can see what you need to tweak to get "in the PH zone" for a girl. You can get PH strips at most health food stores. You can change your PH either by douching or by eating and avoiding certain foods. Which method you chose (you can go with both) depends on what you are comfortable with.
2. Step Two: Change Your PH To The "Girl Zone," And Conceive In A Way That Takes Advantage Of This: So, how do you know your optimal PH or the douche / foods to use to get it? How do you know which sexual / intercourse positions to use and when? I have two sources, depending on which method you prefer (food or douching):
a) Rebecca Washburn's "Pick The Gender Of Your Baby," ebook: There are many decent books out there, but this one is in my opinion among the best because every suggestion is based on scientific fact and research. The author has taken much of the research and work out of this process. She has read all the books, checked all the science, and done the work for you. And, the kicker for me is that she gives a $450 gender clinic douche recipe, as well as the foods to eat, the intercourse positions and the days to conceive.
You'll find no Chinese calenders, experimental herbs, medications, etc. This 75 page book is based on science and she's really done her homework.
b) Ashley Spenser's Gender Selection Ebook is very similar and is also a very great book, but it focuses more on foods to alter PH and does not rely upon douches. So, if you're opposed to douching, this would be a better choice. It seems many people prefer the food route, as this Ashley's Spenser's is the best selling gender selection ebook on the market. Her bio says she used to give seminars on her methods, but as a busy mom herself, she decided to just put what she knew in an ebook instead so she didn't have to travel anymore and be away from her kids. (affiliate disclosures)
3. Step Three: Know Your EXACT Ovulation Day And Conceive During The Window Prior To This And Via The Positions Given In The Books As Directed: I believe that predicting ovulation and controlling PH are the two most important pieces of this puzzle. To conceive a girl, you need to give the boy sperm time to die off before the egg is released. So, you have to know EXACTLY when the egg will release. For that reason, I highly suggest using a saliva ovulation predictor. They use saliva for DNA tests. Why? Because it is extremely accurate.
The clearblue easy ovulation strips I was originally using were not showing ovulation for me. I would run out of strips and give up. When I tried the saliva tests, I found I was ovulating on day 20, but I WAS ovulating, and regularly. These testers are completely reusable, so you can see your varying results from one day to the next, or hour by hour if you wish. They are very inexpensive (under $30), and last forever.
That's it. Repeat this method until you conceive. Read which ever resource you chose carefully to formulate your plan and then be very diligent about following it to the letter. Most of all, have fun with it. This should be an exciting time.