The creativity is half the fun! Browse an art site and look for compositions, subjects, and artists you like. Try out a prompt tool like this, find something that intrigues you, expand on it. Don’t like that tool? Surf random wikipedia articles until you find something interesting:

https://en.wikipedia.org/wiki/Special:Random

Lots of the people on Disco Diffusion have shared their prompts, try searching for “text_prompt” or “my prompt”.