This is a great book for when you are stuck or need to replenish the well of creativity. With a focus on freewriting, exercises often serve as prewriting to get you in the mood to write and open yourself up to new ideas and experimentation.
This one is a classic. Great exercises and prose discussions by the master Ursula K Le Guin herself.
Alison explores examples of non-linear structures in narratives.
This one is a banger. Salesses tears down the old standards about the writing craft and offers a fresh new perspective. Extremely thought-provoking.