Welcome here, pinecone.
If you are looking for one "best book" for framing, you will be disappointed. Framing includes lots of diverse products and procedures. No single author, let alone one single book, covers everything.
I suggest you begin building a library of books on all framing topics, starting with the PPFA bookstore. Their CPF Study Guide is an excellent source of framing book referrals, even if you have no aspirations to earn that qualification.
And take classes. If you are anywhere near Denver, the PPFA chapter there has very good and friendly members and meetings. Get acquainted. Also, save your lunch money and go to the West Coast Art & Frame (WCAF) show in Las Vegas next January. For a few hundred dollars and a few days' classroom work there, you can choose from the industry's best selection of classes, offered by the best educators in the industry. It's fun, too.