Every writer needs a little help some time. So here is a book that might just help. A Writer's Book of Days. I purchased this from Writer's Digest years ago, but it is still available, paperback and eBook format. It offers so much to a writer. Besides supplying daily writing prompts, it offers insight into the minds of productive, imaginative authors along with the opportunity to gain a little insight about oneself as a writer.
It offers the following:
exercises to improve writing
365 days of writing prompts
questions to consider about writing habits and desires
short quotes that encourage and motivate the writer
other writers' experiences
It's a handy little book that I have used privately and as a textbook for my creative writing students. Each student knows to just turn to the page for the day's date if a class day is missed, and the prompt is the same as his/her peers responded to that day. I don't use the other features daily in class, but some days, they are the perfect supplement to the day's instruction.