A blog - http://www.codinghorror.com/blog/archives/001091.html and a book - http://books.google.com/books?hl=en&id=5OhE7dyGtmgC&printsec=frontcover&source=web http://www.paperprototyping.com/

How to do a good prototype - http://tynerblain.com/blog/2010/10/25/a-prototype-is-worth-a-kloc/