You can record as much information as you want, or stick with a bare minimum. Choose to use it as a daily diary, where all your information is kept. Or you can maintain a couple of different books, separating your daily thoughts into one, research and magikal information into an other, with spells and incantations into a third. It’s entirely up to you. But keep in mind, you want your book to be well organized. You want to be able to quickly turn to a particular section and page to find some particular information when needed.