As said before, At Airnet I wouldn't worry too much about book stuff honestly. The instructors do a great job at help you understand everything. If you study 135 FAR's your going to really confuse yourself later. Don't waste the time.
What I would do is relax and clear your head. In ground school, you'll have plenty of time to study, although it is alot of stuff. As well as an entire weekend to practice procedures in the sim before you start your training in it. If you got through the interview, study hard and take it seriously and you should be fine. I won't say it's easy b/c it's not by any means, but it does prepare you to deal with the real world of freight flying. Hope this helps.