Be aware of ways the author shows that specific material is important. Look at the headings. These will help you understand the organization of the chapter as well as help you plan study breaks. The headings tell you every important topic you will need to know after reading the chapter. Notice any author highlighted words or phrases.
Authors use marginal questions, lists of terms, colors, or boxes to highlight information.
These will probably be important vocabulary words or important ideas. Look at the pictures, graphs, tables, charts, etc. They all are included to help you learn the material. If there is no outline at the start of the chapter, leaf through the chapter reading the headings as you go. As you have passed over the material your schema may have been called into action.