The article deals with the principles of designing user interface, focusing mainly on the features of graphical user interface as a dominant form of contemporary human-computer interaction. As non-professionals, computer users come to rely on computer systems to perform more of their basic tasks, it is crucial to provide them with software that makes their work easier and more effective. To achieve this aim the interface should be designed in such away that meets the requirements of a user friendly system: reliability, feedback, error handling, consequence, dialog, transparency, ease of use, user support, help, screen display, and output
