For one thing, we probably learn what writing should look like and sound like by reading. But sooner or later, if we are going to learn to write, we are going to have to stop reading how others write and try to write ourselves. Such advice is almost useless in specific situations. Students can, however, learn a great deal about writing by analyzing how other writers have been specific, compared two subjects, or used fragments. But in order to learn these things, they will need a great deal of guidance from you.
All reading is a matter of interpretation.
Every reader recognizes and remembers what he or she reads in terms of what he or she individually pays attention to and how he or she fits in this information with what he or she already knows. Since every reader pays attention to different aspects of a text and fits this information into his or her own individual store of knowledge and experience, every reading will be different. Thus, if you want your students to read in a particular way, or if you want to be sure that they understand a certain aspect of a text, you will have to teach them how to read the way you want them to. And you should provide them with sufficient context for understanding the reading or make them responsible for understanding the context on their own. If you were required to read a paragraph of theoretical physics in order to pass a comprehension test, you would need to know key terms, you would probably need to remind yourself of what you learned about the laws of physics in high school, you would need some guidance about what in all the jumble of words about quarks and trajectories and subatomic particles was important, what distinguished background information from new information, what made some facts more important than others.