In general, at least under this current DOT standard curriculum, the EMT class is quite easy. I doubt you'll have trouble with any lectures specifically, but many students struggle with some of the psycho-motor skills included in the class. Many programs emphasize memorization of rote facts and acronyms in place of true understanding or analysis of the data presented.
OP, are you asking whether you should study anything particular before beginning your course? If you do a search on these fora you can find good discussions of materials or books that have proven to be helpful.
Are you asking what to focus your studying on during the course? I believe you'll find your textbook while heavy and seemingly long, it has many pictures and is not nearly as dense as you'd expect, and is likely written at a middle-school level. Make sure you read it in it's entirety, as well as any handouts or supplemental materials your instructor makes available.
Hope this helps!