Since I have no prior experience with being a mechanic, is there anything important I should study to help me thrive as a 91B?

Reality check, here. If you have absolutely no experience as a mechanic, why do you want to be a mechanic? Surely there is an mos you would be more interested in.
If you are already on your way to AIT, there's not much more to do other than to pay attention in class and apply yourself. Do your best -- they will teach you from the ground up. Don't second guess them. Do it their way.
You'll be okay.

When you pass Basic and go to AIT that I know you can do it, try to remember how to troubleshoot. Study how the Vehicles work and ask what are thr common problems. You will actually learn more when you get to your unit l. For my time that was 2 years ago if you are a pt stud they give you to choose between H8 (Recovery school) and Airborne.

You need to study the ASVAB book. There is a book called "ASVAB FOR DUMMIES" you can get at a local Barnes & Nobel book store and look for any others that may help you or order if from Amazon or other book stores on-line. Good luck, you will do fine if you start early.