- Pick some sort of metaphorical idea and aim for that, e.g. "This song will sound like different types of water coming together, or arid fire, or have a particular feeling."
To add to this, some years ago I fell into a creative rut. Rather than try to force things out as I stood over my equipment, I gathered a bunch of random pictures and artworks, choose one at random, put it in front of me and I would try to create a soundtrack to that single frame.
It helped a lot. In particular, it really helped me begin to stretch small ideas out into full songs. Instead of trying to ensure that each piece is profound, provocative, and cohesive, I got much better at engaging with my musical ideas as they truly are: just ideas, sketches, imperfect snapshots of an imperfect mind's imperfect experience.
Suddenly, trying to compose a piece that aurally conveys the smell of snowfall doesn't seem as stupid and insignificant, because it just playtime in the end, and every experience is valid if any of them are.
Anyways, the point is really that staring at a picture and trying to make a soundtrack to it is a great way to get out of a writers block mindset or to just experiment with different inspirations/impetuses of creation. And I think still images are pretty key here. Mostly because composing a soundtrack to video can imply or strictly dictate the tempo and rhythmic and ornamental elements whereas a still image will force you to consider those elements abstractly and interpret them.