The first hint books I remember seeing were for the Sierra adventure games of the King's Quest/Police Quest era.  They were small things, more resembling a long brochure than a book, and pretty much the only way to get them was to call up Sierra and order them directly.  They were cheap, too--only $5 or so compared to the $20 you'll plop down for a so-called "Game Companion" or "Solution Manual" today.

The early hint books had a few different sections--the first would just be a big list of how you got all the allotted points in the game.  Next you'd have a Frequently Asked Questions section, and in the back you'd find the complete game walkthrough/solution.  The original hint books--like my 1987 Police Quest book--came with a special decoding ink marker.  You'd scribble over the blank area containing the section you wanted revealed, and the special ink would make the text appear.  This did NOT work very well, as pressing too gently with the marker wouldn't reveal the answers and pressing too hard would ruin the page and obscure the hints forever. Plus, even if you got it to work right, once you revealed the answers once they were revealed forever--not cool if you wanted to lend the book to a friend or start from scratch without hints.

Sierra learned from their mistakes, and later editions came with a tinted-glass thingee that you'd hold over whichever section you wanted revealed (sort of like 3-D glasses).  No mess, no permanence.

Then, later on, everyone started making hint books and everything went straight to hell. 

The thing is, in those days you needed a hint book, because those games were fucking hard.  The hint book you got for them was bare bones, usually just extensive enough to solve the exact problem you had and continue on normally.  I find it pretty ironic that today, when it's nearly impossible to actually get stumped in a computer game anymore (and the chances of finding a good adventure game are virtually nonexistent), games have full-color, 500 page tomes of walkthrough material available for purchase.  Yeah, part of it is because they have to compete with online walkthroughs and FAQs by giving the consumer enough shiny objects for it to be considered a worthwhile purchase, but it really seems as if some games nowadays come with features and easter eggs that would be absolutely IMPOSSIBLE to find unless you had the solution guide sitting next to you telling you how to find them.  It's just sleazy.