Even if you are not a professional writer you probably already heard about writing prompts. They represent a very effective tool for any writing project, so it’s a good idea to know how to use them. (from Daily Writing Tips)
The Red River Valley Writing Project is no stranger to writing prompts; in fact, each morning of the invitational summer institute begins with a prompt.
Certainly you can make up your own prompt, in effect, give yourself a kind of writing assignment.
You can also check out the linked piece above to read more about prompts. And the piece includes online resources for prompts.