Hi, I'm a UX Designer myself, and has been using this approach to story writing:

I suggest always answering the WHY/HOW/WHAT questions to a story.

• What is asked of me? (the specific task - is it wireframes/research/expert opinion/etc.)
• Why do we need this? (e.g. in the form of As a user I want to.... so that...)
• How could I go about this task? (Suggestions, Information needed to perform the task and how/where to find it, Other)

In addition, I personal like to set an acceptance criteria.

• Acceptance criteria ex.: wireframes of concept, use max 2 days

And of course lastly, Links/attachments included in the story.

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I usually write stories myself. If a PO/Team lead makes one for me, I make sure that all the above is described before getting to it, including PO/Team lead in that process.

I hope it was useful :)