Prior to reading this book, I had been studying raw music theory.. very technical and analytical stuff.. on the other hand, the Songwriting for Dummies is the complete opposite of that. It's extremely non-technical, highly unassuming etc.. For example, the authors say that even though knowing how to play a musical instrument would be beneficial, it is not required to be able to write songs. Also the book is more geared towards writing a "Greatest Hit" rather than just writing any old song.. which is why I thought of this book in relation to your question.. It's more of a "things to do and things not to do" type book.
If you want to learn more of the music creation side of things than that is basically music theory then I really enjoyed "The Complete Idiots Guide to Music Theory" for this, more technical, side of the songwriting process.
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