No better way then buying the Redding Study Guide to NCAA Football. I would 1st go thru/study/highlight the chapter on penalty enforcement, then major fouls, then depending on your position, go from there. If you are going to be a deep official, next go thru the kicking game, but if a short wing, maybe the running game would be next. The Redding book is great as it goes into the philosophy of the rules and gives many examples like those in the NFHS Case Book.
I also would recommend the Football Rules Differences Book, which compares NFHS to NCAA rules. It is a great book to see the differences that exist between them, with play scenarios to support the differences.
Good luck, and enjoy!!!