You can use your grimoire as a reference by looking up spells and magical information whenever you need it. You can use it for recording your spells and tracking the results of your spells. A more unconventional, but powerful way to use your grimoire is as an oracle. Ask your grimoire what magic you need to perform today, and open up the book to a random page. Whatever information presented to you is the magic you need for that day. This kind of oracle work is called bibliomancy and is made even more powerful when performed with a grimoire you’ve written yourself.