Funny, I'm memorizing mine for next weekend right now! I draw it out on Paint first of all, with different colors for different gaits. Then I press the back button until it's blank, and the "redo" button so I can watch the test drawn out several times again. I keep drawing it out until I can remember it all.
Last week I memorized my entire test over breakfast just by drawing it out on a stack of napkins. We were at camp and they switched up the groups because of the weather, so I had to have a test memorized to ride for my ride-a-test lesson.
When you have it down, close your eyes and imagine riding through it, in the arena you'll be in, if possible. Think about where your trouble spots will be, where your horse will try bulging to the gate, where he'll have trouble picking up a canter lead, and figure out ahead of time where you're going to have to be stronger with your aids.
All this week and next, I'll be riding my test in my head to get it down pat 100%.
P.S.--If you have an iPhone/iPad/iPod Touch, there's a usea or usdf app that shows you your test in a drawing movement-by-movement format that's helpful.