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.
Discoverability
Discoverability, much like how the word sounds, means the ability of something to be discoverable; it’s the ease that users can find their way around a system and locate certain features. If some things are hard to discover on an interface or the user is easily lost, it may mean that the user flow and information architecture should be reevaluated.
Feedback
Feedback is the principle of making it clear to the user what action has been taken and what has been accomplished. Many forms of feedback exist in interaction design, including visual, tactile, audio, and more. The key is to design the experience to never leave the user guessing about what action they have taken and the consequence of doing so.
Well-designed feedback gives a user confidence that an interface is working as it should and makes the user feel in control.
Conceptual Model
These are things that present a customised idea. People use conceptual models subconsciously and intuitively as a way of systematizing processes. By creating interfaces and apps that echo the way users typically think about completing certain tasks, designers build on existing knowledge and frameworks, making it easier for the users to learn how to use the new product.
Affordances
Affordance refers to an attribute of an object that allows people to know how to use it. Essentially to afford means to give a clue. The physical button on a mouse gives a clue that it can be clicked to perform an action. When an object has strong affordances, it’s very clear how to use it.
Signifiers
Signifiers are aspects of visual design used to represent potential and intended use, and to show the system status. They could be words, symbols, icons, lights, sounds, etc.
Mapping
Mapping is about having a clear relationship between controls and the effect they have on the world. This mapping should feel as natural as possible.
Constraints
Constraints are about limiting the range of interaction possibilities for the user to simplify the interface and guide the user to the appropriate next action. In this case constraints help to clarify interaction, since they make it clear what can be done. Limitless possibilities often leave the user confused.
The Google home page features an extremely constrained design.