The most common approach to line memorization is practice and repetition. This includes scheduling time to study lines, then reading and reciting lines over and over again, until the lines are memorized. Although this technique is one of the most commonly used, and eventually works over many sessions, it is considered one of the least effective ways to memorize information, according to an article published in "Current Directions in Psychological Science." However, the publication goes on to state that all of the traditional methods employed by actors that involve a combination of emotional, intellectual and physical involvement with the material are highly effective methods validated by cognitive research. These techniques correspond with principles taught by the two main acting schools: classical acting and method acting.
Using your imagination is a powerful, technique commonly used by classical actors to assist in memorizing lines. This method entails embellishing and adding details that put you into the scene when rehearsing. It's based on imagining and portraying the external physical details such a how a character walks, talks or performs certain actions. By developing a character and world that the character lives in, it is much easier to memorize lines and far more effective than memorization by rote, according to research presented in "Current Directions in Psychological Science." When employing imagination in memorization, it is important to focus on specific details that help trigger lines of dialogue. For example, you may need to envision the placement of certain objects, the location of places and the reactions of other actors. These are details that you imagine whether or not their presence is noted in the script.
Method acting is a complex technique that requires actors understand the emotional state of their characters and portray that state by drawing on personal life experiences. This technique greatly assists memorizing lines because of the emotional, physical and intellectual requirements involved in method acting. By drawing from personal emotional experiences and then applying them to characters, you are better able to relate to the character, understand why a particular line is being spoken at a given time, and eventually give a realistic performance. Research backs this up as being a highly effective way to memorize information -- since it is easier to remember personal emotions and thoughts, adding this dimension when memorizing lines enables people to more effectively recall information, according to "Current Directions in Psychological Science."
Another component to method acting is creating a motivation behind each spoken line, which will help actors ability to recall and memorize them. Motivations are goals that the character is trying to achieve by stating a particular line of dialogue. Understanding the subtext, or the underlying meaning behind the dialogue, will determine the characters' motivations. Often these motivations are opposite what is being said. By understanding how and why a character employs the script lines to accomplish his desires, you more easily memorize your lines and create a more realistic performance. Because this technique draws from the actor's forging a relationship with the character that includes high levels of personal involvement, it is another highly effective memorization technique, according to "Current Directions in Psychological Science."