Well, MBA.com (part of the official GMAT site) has some good info here:
http://www.mba.com/mba/ApplyEffectively
As for books, here are some. I haven't actually read all of these books myself, but these two have consistently gotten high reviews from users for the last year or two:
ABC of Getting the MBA Admissions Edge (US) (officially supported by McKinsey & Co. and Goldman Sachs)
88 Great MBA Application Tips & Strategies to Get You into a Top Business School
And this one's been around for a while. It's very useful, and my students have found it helpful:
How to Get into the Top MBA Programs