This is what I do and it's way better than any other technique I've tried. Just like burning song lyrics in your head. I recommend doing it in blocks of no more than 7 minutes of dialogue at a time though. Or if it's more spaced out...take it scene to scene.

I did my first semester in acting (college) and we had to choose a scene for scenework. It was from Edward J Moore's The Sea Horse and only the last few pages of ACT I. It was grueling! Took forever to get down. I've started on Williams Uggims from UTBU and I've got most of ACT I down and I've only had the script just over a week.

In high school I used flash cards......worthless!

Learning lines is always a challenge. Luckily, I was in a Masonic youth organization that required lots of memorizing. My grandmother taught me the method I still use.

Read through the whole block of text first (meaning, sentences or scenes, not the whole play, at least, not for learning lines). Then start with your first sentence, or phrase in the case of longer speeches. Repeat that a few times, then say it once more and read the rest. Keep adding more and more in the same method. And if you think you know the next line - go for it! (You'd be surprised how close you can come after all that reading, well, maybe not.)

Another friend writes down the cue lines and his lines in long hand and reviews them at work, then keeps it backstage for review (for the bigger parts).

And there was one person who had trouble getting off-book for a show (he was the detective in a murder mystery). The producer ran lines with him when he wasn't on stage, as did some of the 'dead bodies'. By dress rehearsals he was good to go.

I do not advocate the use of scripts backstage during the run and here is why...

In one show I directed there was quite a morale problem due to "cheat sheets" in use during the run. Several cast members were very put out with (to put it mildly) a cast member who openly used them. They felt it was disrespectful of the show and of the efforts of everyone else who had "done their jobs on time and well" for her to have never fully learned the show. They were also always "on pins and needles wondering if she was going to show up at the right time and say the right thing". No one had confidence in or respect for the "cheat sheet" user. After that episode I do all I can (and have my SM's do all they can) to discourage the use of said... except in extreme conditions..like a last minute repeacement etc.)

Good Luck,

Countbio

Just wanted to add to this  - to the directors.  It's really important to give your actors an off book adtes for lines.  Even break the play into Units (if there are no scenes) and give a date for each. (general rule is - once it's been blocked it should be known).

I realized this when an actor told me 'Can you give me my 'off book' days"  and I said 'I haven't decided yet - just do your best.'  He said 'I need a 'due date' to make myself learn it by then'. - aaah.  Actors are a last minute / craunch time/ kind of people (improv anyone) so you need to give them dates and remeinders.

Also - I totally agree with this: "...how can you even begin to act in the first place? how can you concentrate and be "in the moment" if you're trying to remember what to say?"