I read the book in chunks, out of order (hitting the important bits first), and if on PDF highlight the hell out of it. I also take copious notes on specific rules that strike me as being important.
I’m doing this with Dragonbane right now.
I read the introduction.
Skipped character creation. I mostly referee so save it for dead last.
Read the first half of the skills chapter because it has the core mechanics. Dragonbane is a skill-based game. The second half of the chapter is specific skills and their equivalent of feats, so I went back for that later as part of character creation.
Skipped the next four chapters dealing with combat, magic, gear, and the bestiary.
Read the GM chapter.
Read the intro pages of the bestiary on how monsters work, but skipped the actual monsters.
Read the skills but skipped the feats.
Started on combat.
Etc.
I try to start with the core and build out. Most RPGs are atrocious for actually learning the game. You get maybe a summary of what RPGs are then jump right in to character creation. Blerg.
And I’m always taking notes, summarizing, and quoting the text with page numbers in a separate text file. Like analyzing a text to write a college-level paper.
Most RPGs waste a staggering amount of words vaguely circling around a point or a rule. The use of “natural language” in explaining game rules is a nightmare.