Critical reading applies to non-fiction writing in which the author puts forth a position or seeks to make statement. Critical reading is active reading. It involves more than just understanding what an author is saying. Critical reading involves questioning and evaluating what the author is saying, and forming your own opinion about what the author is saying. Here are the things you should do to be a critical reader.
Consider the context of what is written. You may be reading something that was written by an author from a different cultural context than yours. Or, you may be reading something written some time ago in a different time context than yours. In either case, you must recognize and take into account any differences between your values and attitudes and those represented by the author.
Question assertions made by the author. Don't accept what is written at face value. Before accepting what is written, be certain that the author provides sufficient support for any assertions made. Look for facts, examples, and statistics that provide support. Also, look to see if the author has integrated the work of authorities.
Compare what is written with other written work on the subject. Look to see that what is written is consistent wit h what others have written about the subject. If there are inconsistencies, carefully evaluate the support the author provides for the inconsistencies.
Analyze assumptions made by the author. Assumptions are whatever the author must believe is true in order to make assertions. In many cases, the author's assumptions are not directly stated. This means you must read carefully in order to identify any assumptions. Once you identify an assumption, you must decide whether or not the assumption is valid.
Evaluate the sources the author uses. In doing this, be certain that the sources are credible. For example, Einstein is a credible source if the author is writing about landmark acheievements in physics. Also be certain that the sources are relevant. Einstein is not a relevant source when the subject is poetry. Finally, if the author is writing about a subject in its current state, be sure that the sources are current. For example, studies done by Einstein in the early 20th century may not be appropriate if the writer is discussing the current state of knowledge in physics.
Identify any possible author bias. A written discussion of American politics will likely look considerably different depending on whether the writer is a Democrat or a Republican. What is written may very well reflect a biased position. You need to take this possible bias into account when reading what the author has written. That is, take what is written with "a grain of salt."
By being a critical reader, you will become better informed and may change your views as appropriate.