As an MRT, I found the written test to be the most challenging because you need to know the racquet manufacturers technology terms. Study that a lot.
Also, when you take the stringing section, take your time because I think it's actually an hour you get or maybe it's 45 minutes, I can't remember. Take extra care not to kink the gut. They count off for that. String it at a low tension so there's less chance of breaking the gut. I strung it at 50# for both the gut and syn gut. I was lucky, I took the test on a Wilson Biardo. Love that machine!
Make sure you know how to replace a grommet set and can do it in under 15 minutes. My advice is to take an extra set with you in case you "mushroom" a grommet. Then, you can simply use the new one.
I was lucky, I had Dave Bone (head of USRSA) administer the test and also he gave us a pre-test study session. Invaluable. If you're really serious, consider going to the Grand Slam Stringer's Symposium in the fall in Florida. That's where I took the test and have been there twice. It's a great stringing and tennis experience.
Men's and Women's Head Tennis Coach, Friends University
Dunlop f2.0 Tour, Lux 4G, 4.5 all court, USRSA MRT