One thing that people rarely get to see unless you're already working in the games industry are design documents for commercial games. Design documents usually detail how the game will work or how the story will play out, but there is no "one size fits all" when it comes to design documents.

One of my "Idols" of game development, Al Lowe, creator of the Leisure Suit Larry series among other things, has posted a series of game design documents for several of the adventure games he has worked on. It's pretty neat to read through them and see the kind of details they go over and how they differ a bit from the games that shipped. Be forewarned that most of the games listed are indented for mature audiences so the material in the design documents might not be suitable for all ages.

In addition to that Al Lowe's site is great just for some good stories from the games industry. I'd highly recommend visiting the site and exploring for a while!