Pretty well done. Golf Rules Plain & Simple is a book that I hope only gets better with future editions.
With that in mind, I offer some suggestions that the author or other readers may want to comment on.
While there is a footnote that gives the author's opinion as to the more important rules, he doesn't use them to order his book. Rule #1 (for example) is about seeking advice on golf club selection - and of his five key rule situations - the first one drags in at Rule Number 18. Also, it would seem to be much more helpful to put yellow and red staked hazards on adjoining pages for the reader to compare and contrast.
After stating each rule situation, the author gives the most common mistake made (first) before giving the correct procedure. This is not helpful and potentially confusing. When telling someone how to do something - do you want to start with the wrong way or right way? Nothing wrong with pointing out the common errors - just put it at the end.
Some more could have been expected as to the top issues. For example, how to come to agreement with others as to where the ball last crossed the margin of the hazard. Things to say to an opponent could make this a lot less trying in match play, for example.
To the author, page 67 talks about a provisional ball played for a ball that you think is lost in a water hazard. Agreed. But the more common argument is when it is unclear. Where is your explaination in the book that if you don't see it land (and stay) in a water hazard - the ball is assumed to be lost? Another point that your book appears deaf on - what happens (for example) if you are playing a match and hit a ball towards the woods bordering the fairway. You don't have any indication that it is a hazard (it looks like normal woods from the tee) - you announce your intention to hit a provisional ball as you may have a lost ball. You and your opponent both agree as to where the ball seemed to drop down. You find your ball but those nice woods actually turns out to be a red stake marked lateral hazard. You have a shot to the green (without penalty) that you would like to try. Your opponent says no. He says, "you can't use the provisional ball rule when a ball lands in a hazard. Lack of knowledge of the hazard's existance offers no help. You need to play your second ball (i.e. no longer provisional)as it is the live ball" (in other words, no five options for a lateral hazard). Is he correct?
Finally, while you give the five options for a lateral hazard correctly, a note that "playing it as it lies" also means no grounding of the club (while covered elsewhere) would be a helpful reminder here.
Hope these suggestions help.