A sample can communicate a writing style more precisely than a long list of adjectives. The useful sample shows the structure and level of detail you want without encouraging the assistant to copy unrelated facts.
A practical way to start
Choose a short passage you wrote or have permission to reuse. Explain which features matter: sentence length, paragraph size, vocabulary or the way instructions are ordered. Keep the new subject in a separate section.
Prompt to try
Use the sample only as a guide to sentence length and straightforward tone. Do not reuse its names, claims or examples. Write a new 120-word customer update using only the new facts. Style sample: [sample]. New facts: [facts].
Check the result
Look for accidental carry-over. A sample about a school event should not cause a repair-shop announcement to mention pupils or a venue. Check that the new draft reflects the new facts throughout.
If the result sounds too similar, ask for a different opening and different sentence structures while keeping the same level of simplicity. A style reference should guide the writing, not become a disguised copy.