No matter how clearly you phrase information, no matter how carefully you choose your illustrations, no matter how well you prepare, you are not going to get through to every student on your first attempt.
Instead of getting yourself tied in knots over your failure—which may have nothing whatsoever to do with you—prepare in advance for failures.
When you prepare writing prompts, include in writing stripped-down directions about how to do the main task(s) the writing entails. You can also put the directions in some other formats (audio clips or video), but always put it in writing.
If you include in each writing prompt written information that teaches students how to do one writing task, by the time students have had a dozen writing prompts, they should have a miniature handbook on writing embedded in the prompts.
Encourage students to treat your writing prompts as instructional materials by referring students to directions you included in prior prompts.
Of course, not all students will read the prompts carefully or keep them after turning in the assignment, but if your prompts include genuinely helpful tips, many will hang on to the prompts to use again.
© 2017 Linda G. Aragoni