Steven Pressfield, author of Gates of Fire (the definitive retelling of the Battle of Thermopylae), isn't only a fine historical and military novelist, but an excellent writer on motivation for creativity. His book The War of Art is about the best on the subjects, and the follow-ups he's written to that each have something useful to say as well.
So, a promotional email drops into the inbox saying that a) he's got another creativity-based book and b) that ebook copies of it are free (in multiple formats) for a limited period.
Anyway, the new book's called Nobody Wants To Read Your Shit: Here's Why And What You Can Do About It, and for the present (I can't see an indication on how long this will last, so act fast if you're so minded) it's free as an ebook. The link's here.
Hope you fins the book useful!