Memorization is generally a hard thing for me to do and is probably one of the reasons I did not pursue acting even though I love performing. Everyone has a different tactic for memorization based on what type of learner they are. My friend Aileen, for example, is a tactile learner and has to block out her movements as she memorizes and that works for her. I happen to be a auditory and visual learner, so I have a different approach to memorizing passages.
I first read the page aloud about five times so I get a grasp of what it is I'm trying to memorize.
I then break the passage into different sections, trying to write them down half by memory and half by sight.
I then make the section that appears to be the hardest in a different color, so when I read it off in my head I know it has been "flagged." Then I go through each card and memorize them one by one.
After I've gotten a basic memorization from each section, I recite them all off in order. For the parts that I stumble on I highlight them to serve as a second flag on words that I have trouble on.
At that point I just run through my lines, take a break, and start up again.
Middle English is fun, right?