User interface design of physical interfaces (e.g., buttons and displays) involves knowledge about the features to be provided by a device or application, along with information collected in user and task analysis about characteristics and expectations or the target users and the environments in which the device will be used.
User interface design of the operation of a device or application involves providing appropriate cues to support initiation of tasks and appropriate feedback during tasks to guide the user to successful completion of the task—or to provide a clear indication when a task has not been completed successfully.
User interface design is typically an iterative process, with development of prototype interfaces—which can be drawings on paper, simulations on a computer screen, or initial physical prototypes—and then evaluation of the user interface by project team members or preferably by representative users. Feedback from use of prototypes is then used to refine the user interface design and develop a new prototype. Incorporation of user input early in the design process results in product modifications at a time when design changes are relatively easy to incorporate, as opposed to identification of usability issues when a product is nearly complete and changes may involve significant rework.