I participate in a monthly round robin in the Altered Book club I'm in. Each member picks a theme for their book, and then the books get passed around for everyone to do a spread in, in turn. The theme for the book I had in September was "Nursery Rhymes".
First I scribbled on the pages with brown, green, and black watercolor crayons, then activated it with a paint brush. While the pages were still wet I smooshed them together, and then pulled them apart -- which gave a very earthy, bark like look. My nursery rhyme was the "Nobody loves me, everybody hates me, going to the garden to - eat - worms" chant, which I made a copy of from a book I had bought off the sale table at Borders years ago for super cheap called "I Saw Esau" (full of tongue twisters, obnoxious chants, and word plays of childhood). I drew and painted some worms and stuck them on with those pop up thingies, and glued on a bunch of fall leaves from the dollar store.
A couple of pictures cut out from a gardening catalog, along with the words "let the worms do the work" completed the spread.