When riding any dressage test, don't let the fact that you're riding a test interfere with your riding. Ride around as if you are doing figures and transitions out of your own ideas. I also suggest practicing the test a few times a few weeks before the show to get comfortable with it, know where you're going, what your problem spots are and to perfect your figures.
Make sure you ride everything accurately and if it is accurate and the horse is going well, the judge can give you nothing less than a 6.
In the walk, don't think about making it perfect, just think about letting your seat follow, keeping your horse infront of your leg and even in the medium walk give him a little more rein so he can really reach over his back and stide out.
Also remember to have fun and smile!