Another inspirational book is by Barbara Ueland, and is one of my favorites: If You Want to Write: A Book About Art, Independence, and Spirit, brief at 164 pages, published by bnpublishing (their lower-case, not mine). This was written originally way back in 1938, but nothing that has been written more recently adequately addresses the fears writers face, the inadequacies, all the uphill slog that most writers must battle with before they can ever get a word written. This book in particular is where I would suggest all writers begin, or read if they ever feel low, depressed, or stuck. (The Artist's Way by Julia Cameron is another one that is very helpful about gently guiding you toward creation, but Cameron owes a lot to Ueland.)
Books written by writers are too often self-serving, but I found Stephen King's (On Writing, reprinted 2002, Pocket Books), really helpful, surprisingly so, since he's a horror writer. His knowledge of overall writing principles is very wise, and he is entertaining but sincere in his approach and tone of voice.