Principles of User Interface Design

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There are two Laws of Interface Design (attributed to Jef Raskin in his book, The Humane Interface) that are considered at very early stages. They are based on the fictional laws of robotics created by Isaac Asimov.

First Law	Second Law
A computer shall not harm your work, or, through inactivity, allow your work to come to harm.	A computer shall not waste your time or require you to do more work than is strictly necessary

Once the Laws are complied with and greater granularity is required, the Seven Principles act as suitable refinement. The Seven Principles can be used to guide or evaluate design at any time in the process. In practice, these principles are often re-framed or re-structured to suit a particular company or project, or by professional designers.

Principle	Description	Example
Visibility	Clarity	Is the goal obvious? Icons used?
Feedback	Information sent back to user after their action	Sound? Label showing success or failure?
Affordance	How clear is the use of an element to the user?	Label "Push" on one side of a door; a button saying "Click Me"
Simplicity	KISS principle	Place an Open File option on a menu, under File tag
Structure	Are the elements set out in a meaningful way from the perspective of the user?	Group information within a dialogue box.
Consistency	How easy is it to learn and remember the appearance, positioning and behaviour of the elements?	X to close a window is always on top right hand side of the window; the most important buttons are the same size with only labels indicating different goals.
Tolerance	Prevents user making errors or provides easy recovery or graceful fail	Ignoring of wrong or invalid keyboard input; Hiding options inappropriate in a context.