From our colleague Molly Bloom:
We received many more than we could include in the story so here are some bonus tricks for getting those lines to stick.
The more you do it the easier it gets! Line memorization is definitely a muscle - and you can build it by practicing. I clearly remember a time in college when I was taking several classes and in multiple shows and needed to be memorizing new lines nearly all the time and it was like my brain sort of broke open and it just became very easy to put things in there and retrieve them...of course, I was also a lot younger then.
Don't always start at the beginning. I found that as I practiced a part, I'd have the first act memorized and struggle with the second for a few more days. Start some of your sessions with the second act or later part of the play so all the lines get a balanced amount of attention.
Figure out how you learn and use that to develop how you memorize lines. If you learn audibly, say them out loud and maybe record and play them back for yourself. If you learn visually, write out the lines. I even have a friend that writes out all of her lines using only the first letter of each word. If you learn best by seeing the big picture, map out your character's motives and tactic changes rather than beating yourself up about the words at the start.
While memorizing keep re-reading your lines to make sure you are memorizing the lines correctly. My experience is that once a line has been memorized wrong, it's hard to break that pattern and start using the right line instead. And if you're getting stuck walk through a scene while memorizing; muscle memory is an amazing thing.
-T. James Belich
Develop a physical rhythm and move while saying the lines out loud in a normal volume. Usually I set aside a two hour chunk of time where I can be by myself with nobody around to hear me and I pace and memorize.
I don't like using the term "memorizing" because I favor "learning." Learning about the story, the character, the dialogue. Don't forget to play, play, play! Have fun! In the process, you may just find that your character has a lot more going on than you initially thought!
I like to record the entire play (not just my own lines) and listen to the show on CD in my car or at wherever. I find throwing in some passive memorization helps internalize the story.
As I memorize the lines in the script, I also memorize their placement on the page. It helps me remember the order of the lines, the length of the lines, and be conscious of the pacing of the whole scene. I also count the number of words in shorter lines and look for patterns in repeated lines (since I'm kinda OCD like that).