In helping fellow actors prepare for auditions and shows, I'm always curious to learn about other's preparation processes and to see how I can incorporate better ideas into my own process.
In this post, I'm documenting ideas that I have found help me and my students learn lines accurately and quickly -- both lyrics as well as spoken lines. Part of the challenge here is figuring out how to learn lines well all by yourself -- if you have to do so at very short notice (sometimes overnight!) and therefore may not have the luxury of having friends help you with lines.
Understand the broad strokes first, before trying to commit lines to memory. That is, know the direction of the story, the overall arc of each scene, the main actions/intentions in different parts of the scene/song. This provides a schema into which you can then file the chunks of text you start to learn. It helps my brain hold on better to the things I'm about to memorize. I find that sometimes if I put labels to frame different sections of the song, I have an easier time recalling lyrics. For example, section A of the song is when I'm ranting, the B section is me regretting, and A' is my moment of epiphany.
Check for accuracy early on in the memorization process, otherwise you risk embedding errors into the brain that would only take more effort to undo. There are multiple techniques to check for accuracy, but among the ones that work best for me are: 1) Armie Hammer's process of writing out only the first alphabet of each word you say. There's a method to this madness: it forces you to be very precise and you can no longer get away with not knowing if certain words are elided. For example, 'She's a fair lady' would be written as SAFL, not SIAFL. 2) Once I can get through a scene purely from memory, I either run the scene against a friend and ask them to nitpick me for accuracy, or I type/write out all my words, and then highlight the errors after I compare that against the script. Finding these errors early help you address them before your brain files them away more deeply.
Speaking of the brain filing things away, I have found that sleep is critical to the memorization process! Depending on the person, it can take several episodes of sleep before a scene becomes much more fluid and securely tucked away. This is because your brain trims away excess and does some tidying up while you sleep. If you know you need three episodes of sleep before you are confident, build that into your process. Start learning early enough, and work in enough episodes of sleep so that you give your brain a chance to do its thing after you've put in the work. For last minute callbacks, I've sometimes changed my sleep schedule just to accommodate the learning -- for instance, if I don't have two nights before the audition, I might elect to take a nap, and then wake up to go over the scene again, just to create an extra episode of sleep.
When preparing for a role, I make recordings of the lines against which I would be speaking (with an appropriate amount of silent air-time for me to deliver my own lines). I find the best test for whether my body and brain are truly memorized enough for blocking is if I am able to play these recordings back and have the words still come to my mind smoothly, in an unhalting fashion, while I'm moving about. And I try to do this while navigating the busy streets or subway stations of New York (yes, many a person have probably thought me crazy). Being able to physically move while still delivering your lines is, I find, the real litmus test for readiness. Plus, for me, there's something about moving and going over lines that really solidifies the content. Being able to regurgitate lines while stationary is often not good enough; you may find that your lines may still fall to pieces once the director starts having you move when you begin blocking the scene. Part of the process of learning your lines well is being truly honest with yourself: Am I able to deliver my lines out loud without error, smoothly, and while physically moving? While practicing, how many times in a row can I do so without error?
Reciting lines with a robotic voice can be one way of getting just the text into the brain without also laminating decisions about accents and acting choices -- in case you have to put off those decisions till later in the rehearsal process.
The above is by no means comprehensive, but I hope it can be of some help when the next crunch time comes around.