This book is one of my favorites when it comes to destroying myths about proper language.
Hitchings reviews some of the most common beliefs on what proper language is and how some of them are wrong even if they are continuously propagated by editors, teachers or authors. He explains in a funny and easy-to-read way where some of these beliefs come from (for example the wide-spread “never end a sentence with a preposition” or “do not use split infinitives”) and shows why they are not valid principles to live by when writing in English and how sometimes the contradict common sense or lead to the creation of unnatural phrases.