One way to combat those rough patches is the ever-popular flash fiction writing prompt. Set your main work in progress aside for an hour or a day (or even a week in some cases) and write an assortment of very short stories (fewer than 1,000 words) inspired by random first lines. It loosens the brain muscles and gets your creative juices flowing.
While you can find about a billion prompts online, I've also included a few below.