It will become the practitioner's diary and the memory of the magical journey accomplished. Therefore, keeping it away from prying eyes is very important.
How to choose your Book of Shadows?
According to his tastes: notebook or notebook, leather or cataline binding, loose sheets in a binder, file on his computer...
According to your needs: one every year, several according to the subject (one for rituals, one for spells...), one modular (file or file type)
Just one rule: follow your instincts!!