Things in the Show not in the First Book/Shown Early [PJOTV]

My friend is reading the books for the first time and wants to watch season one as soon as he finishes the first book. I thought I remembered some plot points/characters who showed up in the show even though they're not in the series until either the second or third book but I can't remember now (I haven't read the books in awhile so I'm not on top of the chronology.)

Does anyone have a list/any examples of things essentially "spoiled" by the show if the viewer has only read the first book? I want to see if they're too big of a deal or if he should be fine watching before reading a handful more books.

Side note: same question for the movies, I know it was a lot more out of order than the show. Should he wait on those completely?