The more users' expectations prove right, the more they will feel in control of the system and the more they will like it.

The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.

Consistency is one of the most powerful usability principles: when things always behave the same, users don't have to worry about what will happen. Instead, they know what will happen based on earlier experience.

...pay attention to what users do, not what they say.

On average, when you ask someone to perform a task on a site, they cannot do it. It's not their fault; it's the designer's fault.

To design an easy-to-use interface, pay attention to what users do, not what they say. Self-reported claims are unreliable, as are user speculations about future behavior.

Three Tips: Simplify, Simplify, Simplify.