“How do you remember all those lines?” is the questions actors hear most often, and the truth is that they work really hard at it. And it is, perhaps, the most tedious and seemingly least creative task an actor has. It's also one of the very most important.
I've been impressed over and over again by the fact that the more experienced and accomplished the actor, the more time and energy she will put into the mechanical process of learning her lines and learning them perfectly. Actors with less experience sometimes fall into the trap of thinking they've finished learning before they really have. It's not enough to be able to sit in a chair and run through a scene or speech without a script in your hand. Really, an actor should be able to make dinner or ride a bike through traffic or play a game of frisbee and recite her lines at the same time. You need to have at least that much of your attention available to focus on something besides your lines if you want not only to speak the text, but also act at the same time. If any part of your brain is having to search for the next word, you can't really be in the moment, listen to your scene partner, or engage fully with the emotional ride of a scene or speech.
So how do you get to the place of deep memorization where you could no more forget your lines than you could your own last name? I wish there were magic tricks, but really it comes down to going over them again and again and again and again. Many actors find it productive to move while they memorize: walk or do a light workout on a stationary bike or stair stepper. It can help keep you alert, and rhythmic movement is good for finding and internalizing the rhythm of the language. Moving around a room, coming back to the same area on the same beat, lines or sentences as you repeat the text can also be effective. And, of course, if you can get a friend to run lines with you, that's always a big help.
What about when you come to a passage that just won't stick? I've found that the best thing to do is slow down and ask questions: why does the character choose this word? What about the sound of it and the associations it evokes help further her intention? What is the tactical logic behind the transition from one sentence to the next: are you reinforcing a point? Building on it? Taking the conversation in a new direction because you've clocked that what you're doing isn't working? Are there unspoken thought processes that lead you to what you say next? Are there contrasts or lists in the text? How can you use them to land your argument? Have you taken the time to really visualize the imagery in the text and make it concrete for yourself? Identifying and exploring these elements can help make the text more memorable to you. After a session of working on a piece of text doing exercises on sound, imagery, and argument such as those we describe in the Verbal Arts Workbook, students invariably find that they have a much easier time memorizing. This kind of questioning the text makes the memorization part of your process much more creative and fruitful because it becomes less about cramming things into your memory and more about understanding and developing a sense of ownership of the language.