Unless you are performing a play over the radio, or some other kind of reader's theatre piece, the most obvious required skill of the actor is memorization. Despite the title of this blog, I am of course, not always off book. So how do I get there, when faced with a new script?
There are of course as many ways to do this, as there are actors. Some will read one page or one scene over and over again, for hours at a time, until they have it down by heart. Others will have someone read the other parts with them. I personally find that, when the scene has few enough characters, tape recording myself reading the script, and all of the parts and subsequently playing it back over and over seems to be most effective.
I like this method because it is by listening to a favorite CD or watching a favorite movie many times that I come to incidentally memorize lyrics and scenes, without even intending to. Regardless of the method employed however, you must have the right attitude about memorization.
The moral of the story is to stay stress free while trying to memorize lines. Too many times, actors I know strap their own memory banks into a chair, and try to beat them into submission. While this is going on, they are worrying about how much they have to commit to memory, and wondering if they can do so fast enough. This is ineffective, as worrying about forgetting something is no way to help you remember it.
One way to stay relaxed is to be in character even as you are reviewing lines. Know how they speak, what they are thinking, and how they may approach committing something to memory. This way your mind will associate the process of memorization of the lines with your character. Often you will find that knowing how your character behaves will lead you to more quickly commit to memory what it is that he says.
Do whatever is most comfortable for you. These are just a few suggestions. But by remaining comfortable and relaxed, instead of stressed and worried, you greatly increase your chances of being prepared for that day that appears on every rehearsal calendar; "Off Book Day".