A well designed user interface is comprehensible and controllable, helping users to complete their work successfully and efficiently, and to feel competent and satisfied. Effective user interfaces are designed based on principles of human interface design. The principles listed below are consolidated from a wide range of published sources (Constantine & Lockwood, 1999; Cooper & Reimann, 2003; Gerhardt-Powals, 1996; Lidwell, Holden & Butler, 2003; Nielsen, 1994; Schneiderman, 1998; Tognazzini, 2003) and are based on a long history of human-computer interaction research, cognitive psychology, and design best practices.

Usefulness

• Value: The system should provide necessary utilities and address the real needs of users.
• Relevance: The information and functions provided to the user should be relevant to the user's task and context.

Consistency

• Consistency and standards: Follow appropriate standards/conventions for the platform and the suite of products. Within an application (or a suite of applications), make sure that actions, terminology, and commands are used consistently.
• Real-world conventions: Use commonly understood concepts, terms and metaphors, follow real-world conventions (when appropriate), and present information in a natural and logical order.

Simplicity

• Simplicity: Reduce clutter and eliminate any unnecessary or irrelevant elements.
• Visibility: Keep the most commonly used options for a task visible (and the other options easily accessible).
• Self-evidency: Design a system to be usable without instruction by the appropriate target user of the system: if appropriate, by a member of the general public or by a user who has the appropriate subject-matter knowledge but no prior experience with the system. Display data in a manner that is clear and obvious to the appropriate user.

Communication

• Feedback: Provide appropriate, clear, and timely feedback to the user so that he sees the results of his actions and knows what is going on with the system.
• Structure: Use organization to reinforce meaning. Put related things together, and keep unrelated things separate.
• Sequencing: Organize groups of actions with a beginning, middle, and end, so that users know where they are, when they are done, and have the satisfaction of accomplishment.
• Help and documentation: Ensure that any instructions are concise and focused on supporting the user's task.

Error Prevention and Handling<

• Forgiveness: Allow reasonable variations in input. Prevent the user from making serious errors whenever possible, and ask for user confirmation before allowing a potentially destructive action.
• Error recovery: Provide clear, plain-language messages to describe the problem and suggest a solution to help users recover from any errors.
• Undo and redo: Provide "emergency exits" to allow users to abandon an unwanted action. The ability to reverse actions relieves anxiety and encourages user exploration of unfamiliar options.

Efficiency<

• Efficacy: (For frequent use) Accommodate a user’s continuous advancement in knowledge and skill. Do not impede efficient use by a skilled, experienced user.
• Shortcuts: (For frequent use) Allow experienced users to work more quickly by providing abbreviations, function keys, macros, or other accelerators, and allowing customization or tailoring of frequent actions.
• User control: (For experienced users) Make users the initiators of actions rather than the responders to increase the users’ sense that they are in charge of the system.

Workload Reduction

• Supportive automation: Make the user’s work easier, simpler, faster, or more fun. Automate unwanted workload.
• Reduce memory load: Keep displays brief and simple, consolidate and summarize data, and present new information with meaningful aids to interpretation. Do not require the user to remember information. Allow recognition rather than recall.
• Free cognitive resources for high-level tasks: Eliminate mental calculations, estimations, comparisons, and unnecessary thinking. Reduce uncertainty.

Usability Judgment<

• It depends: There will often be tradeoffs involved in design, and the situation, sound judgment, experience should guide how those tradeoffs are weighed.
• A foolish consistency...: There are times when it makes sense to bend or violate some of the principles or guidelines, but make sure that the violation is intentional and appropriate.