The things that are most important to the course are those that are emphasized during lecture and those in specifically assigned readings. Learn these first and learn them best. General book assignments are important too, of course, and you are responsible for the broad general points that are made in them. But when time is limited, remember that most points on an exam deal with material discussed in lecture.
Facts are the details that many people mistake for knowledge.
Knowledge of a subject means that you can distinguish concepts and facts, and relate different parts. Concepts give you a framework for cataloguing your facts and relating them to each other. Unorganized or isolated facts are merely trivia. If you learn the concepts first, the facts will be easier to remember. But first, you have to make sense of the stuff you wrote down in class.