The War of Art: Break Through the Blocks and Win Your Inner Creative Battles - by Steven Pressfield
This was one of the first books that help me understand how to avoid getting creativity block whether ideas or writing.
The Craft and Business of Songwriting – by John Braheny
Very extensive book highly recommend if you want to go deeper into the craft side.
Didn't read much of the business side as it seems outdated for the independent music movement. Definitely worth reading for songwriting though and this book goes deeper into writers block too!