How can I effectively read a textbook?

Whenever I sit down to read a textbook I find myself highlighting everything and re reading the same line 20 times.How can I effectively read a textbook?
Take this approach, page through the chapter and look at the headings and how it is divided. Look at the end of the chapter for possible review questions or discussion topics and page through it again thinking about which sections you think the answers will be in. Read a paragraph at a time and only underline words not sentences, at the end of the paragraph the words you underlined should make a short sentence that contains the most important information in that paragraph. It is kind of like doing an outline in reverse. the section headings are like the main points in an outline, each paragraph or perhaps a couple paragraphs will be the sub points under the main points. Some textbook authors are just very wordy and redundant and this way you can focus on what the main ideas are and decide if the rest is just window dressing or if it really enhances your understanding of the material. It seems cumbersome at first but when you get used to looking at the material with an eye to pulling out the meat from the alphabet soup it will get faster and easier. Reading college level text books can be a major headache unless you figure out how to cut to the chase.