I ran across this advice on writing prompts on another site a few years ago. They're good tips on using writing promts:
#1: DON'T Limit Yourself to Prose
Unless you're writing for a particular assignment, there's no reason everything you write in response to a writing prompt has to be prose fiction. Instead of writing your response to a prompt as a story, try writing a poem, nonfiction essay, play, screenplay, or some other format entirely.
You never know what combination of prompt and medium will spark your next great poem/story/play/nonfiction essay! Plus, taking a break from writing in the same format all the time might make you think about story structure or language in a different way.
#2: DON'T Edit as You Write
The purposes of writing prompts is to get you writing, typos and weird grammar and all. Editing comes later, once you've finished writing and have some space from it to come back to what you wrote.
It's OK to fix things that will make it difficult to read what you've written (e.g., a weird autocorrect that changes the meaning of a sentence), but don't worry too much about typos or perfect grammar when you're writing; those are easy enough to fix in edits. You also can always insert asterisks or a short note as you're writing to remind yourself to go back to fix something (for instance, if as you're writing it seems like you want to move around the order of your paragraphs or insert something earlier).
#3: DO Interpret the Prompt Broadly
The point of using a writing prompt is not to write something that best exemplifies the prompt, but something that sparks your own creativity. Again, unless you're writing in response to an assignment with specific directions, feel free to interpret writing prompts as broadly or as narrowly as you want.
For instance, if your prompt is to write a story that begins with "The stage was set," you could write about anything from someone preparing to put a plan into motion to a literal theatre stage constructed out of pieces of old sets (or something else entirely).
If you're using a writing prompt, it doesn't have to be the first sentence of your story or poem, either; you can also use the prompt as a goal to work towards in your writing.
#4 DO Mix and Match Prompt Ideas
If you need more inspiration, feel free to combine multiple prompts (but don't overwhelm yourself with too much to write about).
You can also try switching genres from what might be suggested in the prompt. For instance, try writing a prompt that seems funny in a serious and sad way, or finding the humor in something that otherwise seems humorless. The categories we've organized the prompts into are by no means limiters on what you're allowed to write about.
#5 DO Try to Write Regularly
The more regularly you write, the easier it will be to write (with or without writing prompts).
For some people, this means writing daily; for others, it means setting aside time to write each weekend or each month. Set yourself an achievable goal (write 2x a week, write 1000 words a month) and stick to it. You can always start small and then ramp your wordcount or frequency up.