I like to try to repeat the test over and over in my head, with my eyes closed, always works!
This might sound silly, but I set out cones, rocks, brushes, or other similar small things in the shape of a tiny arena, then drill the pattern by myself on foot. It's a trick I learned from my western friends that I've found really pays off for me :)
Work again and again, you will know your test by heart and will be able to focus on your position, your transitions and so on the D day! :)
Drawing it is a good way to memorize it. Also, repeat with your horse of course, or alone by feet. You can represent the test in your head and imagine you doing every steps.
I am not used to do dressage competitions but I guess the key is to repeat again and again your test with your horse or even alone!
Take a paper and a pen and draw the whole test many times, it works well for me.