Well, you can Google for yourself methods of remembering lines, but let me share how we operate to perhaps ease any stress.
- Your words
Usually the lines in scripts are opened to some interpretation. While care was taken to get the words in the script right, generally they do not have to be stuck to word for word - as long as you keep the sentiment of the original lines and flow of the dialogue, all is fine. Adding jokes may or may not be appropriate, and some words may be written as critical references to other parts to the script, so always check first if you have changes in mind - it may add or detract from the message and you don't know it. - Promptings
There are ways you can hide scripts, or get promptings, during a presentation, but use it as security - not in replacement of learning lines. Just mention it to the director.
Cards hidden, a computer screen facing you, someone sitting at the base of the stage to call out, an ear piece and someone prompting you (tricky, try it first) OR props written into the script that hide the script like a newspaper, or phone or inside a box.
Just avoid reading out the lines while you act. See them, get prompted, and then look away and say them. - Repetition
Generally, repetition works. As hard as a script seems to begin with, put a bit of time in and you should start to find the words coming back to you. - Sections
Try learning little sections at a time well before moving on ot the whole script. - Methods
See if any of these work for you:
-record the script audio and listening to it over and over.
-draw the script in cartoon form so you can visualize where the dialogue is going.
-filming it and watch it over and over
-make sure you rehearse it with others, and while doing any required actions. - It's not Shakespeare
People do not know the script. So when things come out differently, or ad-libbing comes to the rescue, most of the time, no one watching ever knows! As long as you know where the drama is meant to head and what the ultimate message is just keep rolling.