According to Janet Burroway's classic "Writing Fiction: A Guide to the Narrative Craft," the four methods of direct characterization are speech, action, appearance and thought. A fifth method of characterization, author interpretation, is classified as indirect characterization.
Direct characterization provides the readers with described details of a character that allow the readers to interpret the character themselves. This modern narrative technique is based on the idea that real people and characters alike constantly reveal things about themselves through nothing more than their words, body language and actions.
There are a few other methods of direct characterization. Some scholars split character action into both action and reaction, for instance. Others add speech and thoughts of other characters or the character's surroundings. However, these extra methods can easily be included under the primary four.