Check out the Something For The Weekend threads. Every two weeks our @davescm puts up a starter image, which is usually a Blender/Substance render, and anyone who wants to join in can upload their interpretation of that image. It often works out that my creative ideas are not there when the image first goes up, but ideas come from other people's uploads or from the banter between participants.
Another benifit is that you tend to hone your skills and learn new ways of using Photoshop. People are always happy to explain how effects were done, or you might have an idea that you need to think about to make it happen.
Or you could stick around and respond to a few threads. The hardware and other fault related threads are not very exciting, but the 'how to do this effect' threads can get you thinking. It all adds to your Photoshop toolbox.