I have gathered these tips and hints about creating Altered Books off of various email lists that I am on. Hope these help all of those folks who are entering into the world of Altered Books (me included!).
From Nicole M. Wolverton: I love making altered books and the best advice I can give you is to start with something simple. Start with an idea - an easy one would be to do make a book devoted to love. Now go to your local Borders, Barnes and Noble (to take a look at the bargain book aisles) or a used bookstore - look around for a hardcover book that will go along with your theme. You could get a bodice ripper type of romance novel that will obviously have a lot of words you can use in your book design, or you could get a medical text that has a chapter on the heart, or a self help book about relationships, you get the idea -- just think creatively! OK, so you have your book, look through the book and find pictures you'd like to use or text you'd like to use and mark the page with a paper clip so you can find them easily. Start thinking about if you'd like to design the cover before or after you alter the pages, or if you'd like to rebind the book, now start visualizing how you'd like your theme to play out in your book. I have a tendency to make a plan first, and then go and glue all the pages together that I want glued, cut pages up, cut windows into pages, etc, and then I'll start altering the individual sections, you may work better making it up as you go along.
When you're ready to start working on your pages, the best things to have close by are different colors of gesso, glue, acrylic paint, random ephemera, tags, and lots of ink and stamps. My favorite way to prepare a page is to mask whatever elements on the page I'm using (text or pictures), and then gesso the page (around the mask). When the gesso is dry, I rub Adirondack dye reinkers onto the page and then remove the mask and then I work from there.
As for getting over the idea that books are for reading, not for tearing up, well, obviously you're not going to use a first edition Alice in Wonderland or something like that. I make it a policy to alter books that are no more expensive than $5.
Once you get started, it really becomes obsessive - good luck!