As a Product Owner your main duty is to keep Product Backlog in a great shape, in condition which is enabling developers to work on PBL items. So, this is what you need to take care about:

1. Keep user stories prioritised – uniquely. There can’t be two user stories with the same priority.
2. Keep your user stories READY (by Definition of Ready*) at least two sprints ahead.
3. Keep your user stories granular enough for the team to finish each user story within a sprint.
4. Keep your user stories grouping – may each user story belongs to feature set/epic/theme.
5. All user stories for at least next two sprints should be estimated by the team. Preferably, have all PBL user stories estimated (at least roughly).
6. All user stories for the next two sprints must have the acceptance criteria.
7. All future user stories or epics must have at least feature acceptance criteria.
8. For all user stories for the next two sprints keep list of necessary resources. Keep critical resources marked RED.
9. Keep all items (technical tasks, bugs,…) prioritised and READY
10. Keep all user stories for the next two sprints refined by the development team.

*Definition of Ready – each user story needs to fulfil these criteria to be accepted as ready for the development

• User story has: title, description, acceptance criteria.
• User story has all necessary resources prepared.
• All user stories which original user story is dependent on are done.
• User story has unique priority defined.
• User story is accepted by the development team.