Design for regular, blank, and error states
For each screen, you need to consider three possible states:
The screen people see when everything’s working fine and your app is flush with data.
The screen people see when using the app for the first time, before data is entered.
The screen people see when something goes wrong.
The regular state is a no-brainer. This is the screen where you’ll spend most of your time. But don’t forget to invest time on the other states too (see the following essays for more on this).