Here are some of the things that have worked for me.
1. Build a camera out of a sardine can or some other common object for the purpose of photographing some kind of space or place where a conventional camera can't include enough. If you've never made a pinhole camera (note: MADE, not just used one you've bought), it gives a whole new perspective, photography as sculpture.
2. Expose a roll of film or two with no part of your body touching anything solid.
3. Have someone blindfold you, take you to an unfamiliar place and lead you around while you use whatever vague clues that might stimulate you to think there could be something to photograph there.
4. While we may think it "shouldn't" matter where we are, going to someplace different with no particular kind of image in mind often helps. It doesn't matter where, so much. A few of my most memorable images were made on trips to places like little towns that just about everyone thinks are boring.
5. When I was doing long night-time commutes, I kept myself awake by shooting blind out the window of the car while driving (do NOT look through the camera!) It was surprising what I came away with.
6. Set the camera up in a dark place, maybe the darkroom, on a tripod. Positioning yourself in front of the camera and draw in the air with a light pencil. A "maglite" type flashlight with the reflector removed works great for this. Try moving slower or faster to vary the lines quality, and toward the camera or away from it to change the size of the line. This is amazing to do with a pinhole camera. If you try the pinhole, be sure and move the light in very close to the pinhole sometimes. You will be surprised.
7. Go to a place distinguished by your total conviction that there could not possibly be anything there to photograph. See what calls you. My wife and I once did a workshop where we chose a single block in a very desolate industrial area devoid of anything that seemed at all interesting. It was amazing what people brought back.
8. Have someone else select images from your proof sheets, and print the ones they select. These are the ones you aren't seeing, and you could perhaps gain a new insight into your work.
Some of these suggestions turn photography toward a rather kinetic activity, but sometimes, that might be just what we need. There are no guarantees. I often hit the skids, sometimes for extended periods. Everybody does.