Brian Eno and Peter Schmidt explored this exact problem with their Oblique Strategies, a series of prompts and thoughts designed to break loose of repetitive processes and loss of creative thinking. Here is a handy web application that shows you random picks from the strategies (and there are several others if this link goes down).
Brian Eno discussing the strategies, in 'Keyboard' magazine, 1981
"Most of the Oblique Strategies deal more with approach than with specific techniques, so in that sense they imply a philosophy about working. As the list became longer it became more unwieldy, so I transferred the ideas onto cards about the same size as playing cards. During recording I would pull a card at random and spend a few minutes pondering how the message on the card related to what I was engaged upon. The usefulness of this exercise is that it temporarily removes you from the nuts and bolts of what you're doing. It asks you to reconsider the work on a conceptual level. Often I decided before pulling a card to accept its advice even if that advice seemed distinctly inappropriate. These occasions have proved to be some of the most pertinent uses of the cards. Shortly after I had transferred the list onto cards, I showed them to my friend Peter Schmidt, the painter. It transpired that over the previous few years he had been making a similar list, and that our two lists contained a number of almost identical propositions. What was so interesting was that many of our ideas were transferable. Strategies that he had evolved in relation to painting made sense musically, and vice versa."