The user stories are the guarantee of a good conversation and for this to happen correctly you must know how to write user stories, this video will tell you the basics, the topics you should know and then you can read about each of these topics, such as:
Criteria of acceptance
the triple C
The INVEST model
When creating user stories these should be
INDEPENDENT
NEGOTIABLE
VALUABLE
ESTIMABLES
SMALL - SMALL
TESTEABLES

And most important of all:
User Stories should generate an excellent conversation