Donald Norman, one of the most notable researchers in the field of human-computer interaction and user-centered design, provides six key design principles to keep in mind while designing any interface. Norman’s idea is that devices, computers, and interfaces should function correctly and be intuitive and easy to use. The six principles that revolve around this idea are:
Users should know, just by looking at an interface, what their options are and how to access them. This is particularly important in mobile applications because it is a challenge to make everything visible within the limited screen space; hence, it is essential to include only the options that are needed. For example, a log-in screen only needs information about logging in or signing up, so cluttering it with other information would go against the visibility principle.
The user must receive feedback after every action they perform to let them know whether or not their action was successful. For example, changing the icon on the tab to a spinner to indicate that a webpage is loading.
Affordance is the link between how things look and how they’re used. For example, a coffee mug has high affordance because you instantly know how to hold it just by looking at it. The same is true for digital applications; the design should be intuitive enough that the users know how to access their desired information just by looking at the interface.
Mapping is the idea that, in a good design, the controls for something will closely resemble their effect. This is best understood with the vertical scroll bar; it tells you where you currently are, and the page moves down at the same pace and sensitivity as the vertical bar. A non-digital example is of a modern stovetop whose control knobs are arranged in the same order as the burners. This way, you will know exactly which knob operates which burner.
Constraints restrict a particular form of user interaction with an interface. This is essential because the user could become overwhelmed with the range of possibilities available through an interface. An example of a constraint is an online form that does not allow users to enter letters into a phone number field.
People learn new things and manage better when they recognize patterns. Consistency is key for these patterns to be recognized and learned by users. If similar-looking things do not produce a similar output, the user is bound to become frustrated. For example, if a website’s buttons are protruding boxes with labels on them, then all of the website’s buttons should look like that. Similarly, if a backward arrow denotes the back button, then it should not be changed to something else because that would be inconsistent with what the user has learned.