Major areas are
- Installation of the application.
- First time launching an application without having network access.
- Uninstallation of the app.
- The orientation of the app if it is supported.
- Testing application performance on different kinds of devices and network scenarios.
- Testing the application response and how it responds when an invalid user credential is provided.
Also, if your application is accessing any network then you must check the logs generated during that period so that the sensitive information should always go in an encrypted form.