The word "effective" depends on the type of the book.
If the book is a reference book, "effective" means after reading the book, I know where to look for answers
Reference book as a set of tools that add up to my toolkit, and use whenever I need
E.g: Design Patterns, Refactoring, etc
If it is not a reference books, "effective" means after reading the book, I learned the knowledge shared in the book
Non-reference book as techniques that I actually learn. I do not have to spend extra effor to use them, I learned them and have them will me all the time