There are a number of approaches to helping students organize their thinking and get the most out of textbooks. Some of the strategies, such as the SQ4R process, are useful in upper elementary, middle, high school, and college levels.
Also, having the students complete simple text summary activities can help you get a better idea of which aspects of comprehension they find difficult. Our sister site, Adlit, has several summary sheets available, as well as an excellent library of comprehension articles.
Finally, the Learning Strategies Database at Muskingum Colleges Center for Advancement of Learning (CAL) has a very useful website. It has an extremely comprehensive listing of reading comprehension strategies applicable to both secondary and postsecondary instruction.