The Rules of Spanish Spelling
The Spanish letter z can change to c: voz, plural voces. It's similar but not the same for j and g. When is the letter u silent in gu? When are b and v pronounced like English b, and when like v? When do pronouns join onto verbs? Why is there an acute accent on llamó but not on dio? When does mi have the acute accent and when not? This short book answers your questions with a minimum of jargon.