Study philosophy. In the classical era, Plato and Aristotle provided the two main philosophies regarding art and its purpose that were the guiding forces to literary criticism. Plato believed that art should mirror life and teach its readers, and abhorred the use of fantasy and lies. Therefore, Plato would view any work of fiction as low art. Aristotle saw the importance for not only mirroring real life in art, but the use of imagination to tell a story. So, Aristotle would have given more credence to fiction as well as non-fiction.
Learn the historical context. Most historical literary criticism places emphasis on the era and political influence on art. These critics choose to look at art and attempt to understand it by searching the history of that time and the sociological status of its author.
Understand the literary work's effect on the audience. Criticism can also be seen from those who follow the affective notion of a literary work. By looking at the intended affect on the audience, and how well it matched up with the author's intent, this vein of literary criticism judges a piece of art accordingly.
See the literary work as an object free from any other determining factors. Criticism is sometimes taken on by those who don't care for the way a work mirrors reality, affects the audience or adheres to historical fact. Literary criticism of this form looks at the content of the work along with the form, syntax, dialect and phrasing.
Read the historical, biographical and political information from the period in which the work was written. Understand literary criticism by learning everything you can about the author and where they stood in their world when they wrote the piece. This includes their influences and their social status.