Principles of usable design apply

Consistency - similar tasks done in similar ways.
Compatibility - compatible with users' expectations.
Consideration of user resources - accounting for demands placed on users.
Feedback - actions acknowledged and results indicated.
Error prevention and recovery - error likelihood minimized and recovery easy.
User control - control over actions taken by the product.
Visual clarity - effective presentation of information.
Prioritization of functionality and information - most important is easily accesible.
Appropriate transfer of technology - application of technology to enhance usability.
Explicitness - functionality and operation is clear.

Reference:
Jordan, An introduction to usability, 1998.