If I were you, I would read (and this should be sufficient IMO):
Dr. J. Fuhrman - Fasting and Eating for health
H. Shelton - Fasting can Save Your Life
The first one is more up to date I believe. Tough it is not much rich of details on “how to do” a fast on your own. In the end of what it’s written in the book, you should see a professional MD to go on a fast safely. (I read this one)
Shelton’s however should be read if you want a more detailed guide (I didn’t read it).
Interestingly, Fuhrman states that hypogonadics should’t fast as he saw many hypogonadics going in troubles with fasts. So be carefull as some of us suffer hypogonadism too, as I do. High intensity physical activity however appears to be restoring my T levels and functionality, so I’ll prosecute this way and see If I get back to normal before taking the risk of a fast.