tips for autograph books:
autograph areas smaller then 4x4 are hard for the head characters to sign (Mickey, pluto, minnie, etc), and face characters (especially princesses like big spaces for a flourishy autograph
organize your book - either by movie or alphabetical order
any spiral bound book will work well, I've bought some nice ones over the years from Borders but I believe Michael's has some nice 6x6 books
google Disney clip art for some good images of characters
stickers also work well for more common characters - can be found at Michael's, ACMoore, Hobby Lobby, Target,
Walmart - look in the giftcard section for small stickers
add your email address and/or mailing address to the inside cover in case it gets lost
customizing the book per child is all personal preference. My DD loves princesses so hers is very girlie. the boys love Goofy, Mickey, and Donald so their books match their character. Adding the kids names to the cover is fun, have them help decorate the cover or if it's a surprise find out who their faves are.
make sure you leave one side for a photo and the other side for the autograph. Some characters don't sign though, like Beast.