There's not really a good resource for knowing what to do before a steno speed test besides what your teachers and other professionals in the field can tell you. For this reason, I've consulted some sprinting/running sites because that's pretty much what we're asked to do on test day. We're not running a steno marathon; we're hanging on for dear life five minutes at a time.
What I've found out is that the final few days before and what you do with them can make or break your testing day. The number one thing I hear is to get a good night's sleep, and I'd say that applies to at least the week before the test and especially the night before. But don't sleep too much! It could make you groggy.
I've also heard not to practice or to just do a light sprint practice session the night before so your muscles are rested, primed, and ready to go. I know that when I practiced like mad the night before a test, I always seemed to do less than stellar the next day. But by all means read over your briefs, phrases, and trouble words as much as you can for the days leading up to your test. Sometimes we can forget just how much of steno is mental.
And don't break your routine. If you drink coffee every morning, don't skip it on test day because you think it'll help. It won't. You'll get a nasty caffeine headache and probably not perform your best. Avoid changing your equipment on test day unless an emergency dictates that you adapt. Don't overeat or carb-load the night before or day of. Don't forget to stretch your forearms the night before and day of if you're not already doing it.
Pack all your gear the night before, and make a checklist so you don't forget anything. Last but not least, relax. It's probably easier said than done, but we're more likely to perform our best when we're not putting too much pressure on ourselves. I'm planning on approaching this Saturday as if it's any other depo that I'd walk into where I'm cool, calm, collected, and ready to write my best.
Good luck, test-takers! May the steno force be with you!