Don't bother trying to prepare beforehand. The math on the enlisted side is not advanced (basic algebra, exponents, logs, and trig). You'll learn the way the Navy wants you to learn. When you get here, develop your study habits early in A School, so the rest of the pipeline will go by much smoother. It's not as hard as some people make it out to be. Nobody wants you to fail, and most of the instructors care about your performance, as long as you put forth the effort and aren't lazy.