Principles of User Interface Design

What would be the essentials to developing a successful user interface? An early study sheds light on some of the principles of UI design:

Know your users and the systems currently used by your users; make sure there is consistency in behaviour throughout the UI; utilize visual feedback in the user interface to reflect changes; have multiple ways for users to accomplish tasks; understand the rules of the “language” of your UI design; place importance on providing ways to minimize the effects of user mistakes; provide Help that is appropriate to the users and tasks; understand the role aesthetics plays in a satisfactory user experience; and test your UI design solutions with actual users.