When you model use cases in the UML, every use case should represent some distinct and identifiable behavior of the system or part of the system. A well-structured use case
Names a single, identifiable, and reasonably atomic behavior of the system or part of the system.
Factors common behavior by pulling such behavior from other use cases that it includes.
Factors variants by pushing such behavior into other use cases that extend it.
Describes the flow of events clearly enough for an outsider to easily understand it.
Is described by a minimal set of scenarios that specify the normal and variant semantics of the use case.
When you draw a use case in the UML,
Show only those use cases that are important to understand the behavior of the system or the part of the system in its context.
Show only those actors that relate to these use cases.