The Zettelkasten note-taking method has made book writing and writing scientific papers easy for hundreds of years already.
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When taking book notes on paper, I find it useful to start by drawing a vertical line down the middle of the page. On the left I write ideas and information based directly on the book, including but not limited to direct quotations. On the right I write thoughts that are triggered by the reading but may be only peripherally related to the book's actual content. That way if I decide to write a review or some other text referencing the book, I can easily keep my own ideas separate from the author's.
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