hmmmm. I work in stories in my head, and I am not a succinct type of person so I rarely can tell a story/idea with just one picture. That said sometimes I feel blocked too (okay, quite often).

Sometimes I deliberately choose something that has “multiples”. for example, when I wanted to practice watercolors, I wanted to do something long enough to be able to start understand the medium. I thought of different little portraits I could do, and then I thought about the different incarnations of The Doctor in Doctor Who. There’s 11 of them! To complete the project I would have to do 11 portraits. That seemed like a good way to start and I didn’t have to ask myself, “who should I paint next?” because I knew already, so I could just focus on painting and learning the medium.

I suggest you pick a larger theme, something that inspires you right now: The ocean, forests, museums, books, etc. Something big and rather vague. Then make a list (yes a list!) of the things you love about it, the things you associate with it, from objects (seashells, pine trees, insects, etc.), to insubstantial things (loneliness, happiness, wistfulness, etc.) to colors, etc. Anything.
I find that when I do that, there are themes and pictures in my head that start emerging, work on these ideas and separate them into however many paintings/artworks you need to do.

That’s one way, among many, to go at it. If you are still blocked you can choose something more fixed. Like if you need to do 7 artworks, for example, you can start with something that has 7 multiples, like the days of the week, and go from there.

this is long, sorry. But I hope it helps.