Definition of Done: Define common acceptance criteria for your stories
Describe default requirements for all your stories. Avoid technical dept.
General acceptance criteria define your Definition of Done (DoD). Usually a definition of done contain non functional requirements which need to be fulfilled by every story as well as testable requirements and limitations. The DoD is an agile document that requires regular adjustments and reviews.
A good DoD describes the depth of documentation, testcoverage and performance expectations.
Small, but can be complicated.
It can be hard to keep the Definition of Done in the minds of the team (esp. if the DoD is to generic and does not fit to the current state of development). It is upon the Product Owner to insist upon the compliance towards the DoD.