Outlining your textbook can be difficult. What do I write? How should I write it? How much is too much? The answer is there are no answers. Each person will learn to write textbook outlines in the best way for them. This is why I did not title this post "How-To...", this is what I've found to be the most effective way of textbook outlining.
I Read through each paragraph without writing anything, just reading. Then after I read the paragraph or section fully I go back and highlight what stood out the most to me, what was the most clear concept in my brain. After doing this through the entire chapter, I begin my outline.
I've found that the best way for me to visually outline my textbook is by the titles the book gave. It makes it super easy when I'm doing any homework for the assigned class since it's usually set up in order of the book.
I use "Heading 1" in One Note for each major section; "Heading 2" for each branch off of the major section; and "Heading three for all subtopics within those sections. I always do my readings before the due date, so that while I'm in lecture I can star anything that the professor mentions is important. One note makes this easy because of the different tags they offer for lines of text:
The most important part of outlining a textbook is not to use the language word-for-word in your outline. Make sure you write in language you can easily understand. I also find it easiest to use bullet points. Writing in full sentences won't necessarily help you understand the specific details of a concept. But using bullets can help you quickly learn to categorize information to their correct topics. This is especially helpful in courses like economics where multiple terms have multiple definitions and are covered under multiple topics.
What's your system for outlining?