Do not take these readings lightly. For example, in the past I have based an entire ninety minute discussion on a primary source as short as one paragraph. To sum up, the only way you are going to get through all the reading is to approach it with the proper attitude, something I have already discussed. Most instructors assign readings because they want their students to read. Lectures are one thing.
Books are another.
And whether your instructor assigns textbooks, monographs, sourcebooks or even novels, the above rules all apply. One last thing. Feel free to assess the assigned readings. Although end of semester course evaluations often contain a section where the student can assess the books, why not tell your professor as you are reading the text. I've always had the habit of asking students about the books while they are reading them.