Imagination is not two dimensional. When inspiration for an idea is elusive, take an item--anything--a favorite song, poem, fairytale, painting, or natural object, for example, and twist it around in your mind. See it as a multi-faceted crystal. Do you see something different about the same old subject matter by looking at it from a different perspective?
Let's use the example of author Madaline Miller's books, The Song of Achilles and Circe. It's easy to roll our eyes and say that mythological stories are old and boring. But she looked at them in a new way. As a storyteller, she examined those stories like a gemstone, and in turning them over in her mind, discovered a new and interesting way to tell the tales of legendary characters who've been studied almost ad nauseum for thousands of years.
In your own work, look at things from a different angle. Remember in Dead Poets Society when Mr. Keating had his students stand on the desk to get a different perspective? Ask yourself "what if?" What if you composed that song in 3/4 instead of 4/4? What if you left the arms off that sculpture and concentrated just on the torso? What if you tell the story behind the story (watch Shadow of the Vampire to see what I mean). What if you designed that piece of jewelry, clothing, etc., using the "wrong" side of the material out? What if an artificial limb could be controlled using brain waves? There are no mistakes or limitations in imagining what could be. Philosophers and physicists call this process Thought Experiment.
Are you blocked or not sure if your project is on the right path? Twist the idea around in your head and ask what if? The solution will come to you in time.