Re: Reading Game Manuals
I always read rulebooks through at least once to get a feel for the way the rules integrate with one another and to get a feel for the author. This latter can be invaluable when it comes to interpretation of obscure rules. The more knowledge I have of the author's mindset, the easier it is to fill the inevitable gaps in his/her rules.
Having said that, I generally skim or skip any 'what is an RPG' and 'how to be a GM' sections at the beginning. I also tend to avoid the ninety plus pages of narcissistic exposition where the author drones on about his/her quirky game world that I'll never use. Unless those sections are used to provide thoughtful examples of the rules in play, of course. In fact I tend to avoid altogether rules that include large tracts of game-world narrative. Why should I buy pages I don't want to use?
These days I play almost exclusively in online PbP games, so the rules have to be very simple to reduce turn-length - rules-lite games are my favourite. Consequently, the rules I entertain are seldom more than twenty or thirty pages long, and some are contained on a single sheet of A4. It doesn't take much to read them through.
If I'm using a longer set, after reading it through I'll re-read the sections I need for immediate game play - Chargen, combat, intrigue, whatever fits my game. Then I'll make comprehensive notes, insert a number of modifications and houserules as I deem necessary, and then make brief notes and reminders of the lesser-used rules. After that, I can pretty much put the 'great tome' away, play from my notes and only bring the book out if I need to check something.