Nielsen's 10 heuristics

Jakob Nielsen's heuristics are heuristics used for ensuring proper usability in interface design. The heuristics were published in 1994 in a joint effort with an associate of his and are still widely used to this day with no changes whatsoever:

1 - Visibility of system status: System should always keep users informed about the inner proceedings and provide immediate feedback for every action the user performs.

2 - Match between system and the real world: language used in the system should be intelligible to the user with little to no cognitive effort involved. The elements in the system should follow a logical order and its interface has to follow common conventions to the user, like using a red colour for danger signs and yellow for warning and green or blue for dialogues informing the user that something has occurred as expected.

3 - User control and freedom:  Upon making a mistake, the user should have an easily identified way out. Support for redo and undo operations is the norm for accomplishing this heuristics.

4 - Consistency and standards: users shoulsn't have to wonder what to do next due to lack of consistency between one screen and the other. The human capacity for pattern recognition should be fully exploited in order to not baffle users with screens and dialogues that differ from previous ones. After executing a certain task and advacning onwards to the next step and a new screen is presented, the newest screen shouldn't dissent from the previous one in layout.

5 - Error prevention: make sure your system is as bug-free as possible. Either eliminate error-prone conditions or check for them and present users with a confirmation option before they commit to the action.

6 - Recognition rather than recall: this dovetails nicely into the consistency and standards heuristics. Users should instinctly grasp the meaning of the interface without resorting to his memorisation skills. Everything needed should be presentable within the user's field of vision. Instructions for use of the system should be visible or easily retrievable whenever appropriate.

 7 - exibility and efficiency of use: System should cater to both experienced and novice users. Efficiency of use means that users can tailor the system to perform repeating tasks.

8 - Aesthetic and minimalist design: Dialogues should not contain information which is irrelevant or rarely needed. Every extra unit of information in a dialogue competes with the relevant units of information and diminishes their relative visibility.

9 - Help users recognise, diagnose, and recover from errors: error messages should be written in plain language without befuddling string combinations (see microsft windows error codes for a counter-example). Besides, they should point to the proper problem and accurately describe a solution.

10 - Help and documentation: Should be easy to get to and relevant to the current task. Again, concision and coherence need to be observed in order to design effective in-system help.