WHAT MAKES AN EFFECTIVE INTERFACE?

I reckon I have a quite good question here; it helps me a lot. I found a word-press user page who provided lots of information how we designers should build the interfaces for a specific user-group.
Link : http://iface.wordpress.com/2006/02/09/what-makes-an-effective-interface/

Here are his useful tips in summary.

Conclusively, we can say that an interface should

• Talk the client’s language
• Specify the information expected from the client
• Provide information about the service (only the information that is relevant to the client) that the client can expect.

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Yes, one more time, I think about it and decide to change my user-group; it will need to be more specific and clearer in order to be easier for me to design my interface