First it’s important to know that there is no one and only Book of Shadows. This concept is a fictional plot device to explain why magick is not effective without THE Book of Shadows. The idea is that if you just have the right book all your magick will be effective. This usually sets up a dynamic between the characters where each tries to possess THE book.
Actually, the name simply refers to any book or digital folder that contains a witch’s personal spells, potions, references and records. The truth is that any given magycal rite or spell is effective only if it’s effective for you. Another witch’s Book of Shadows is likely to be useless for you.
To that end, you will want to gather any and all information that works best for you. Places to look are books, online, from other witches, and even your own dreams.
How can you tell if something will work for you? Try it.
Of course, there is so much information out there no one can try everything. What I do is examine a new piece of information and notice how it feels to me, how it fits with what else I’ve learned. If I am invoking a deity, I ask myself how do I relate to this Being in the context of my workings. If I am looking for correspondences (how one aspect relates to another) I ask myself if the whole package seems to fit together nicely. For instance, I might choose to work a love spell on a Friday night because that is the traditional time for working love spells, under a waxing moon. I might choose to evoke the Goddess Diana. I may then choose to write a spell using metaphors of the hunt “hunting for love”. I might then choose to burn red rose petals in a fire made with red oak wood. To me, everything on the list fits together, each item reinforcing every other item. What I gather for a particular working may not work so well for everyone. In fact, I’d be surprised if it did.
So don’t let anyone tell you that you HAVE to have a certain book. Use what feels right. I use a journal that I got many years ago. It looks really girly but I like it.