How to explain "achieving good Usability"

I have a quite hard task right now: I need to explain agencies and graphic designers, how to design a usable website concept and visual design.

The goal is to give designers a workbook/tips&tricks/FAQ/guideline for make their design drafts quite usable, before it will be tested with users somewhen. Like a sort of quality check. In order to avoid multiple redesign iterations. (I'm not talking about specialists like UX-, IA- or IX-designers.)

There are guidelines for good usability like Nielsens heuristics or ISO standard 9241-12 and 9241-110, but its still relies on experience with usability. Or in "usability-word" it lacks of self descriptiveness. It is not clear for a designer, what this guidelines mean. Actually they are like the Gestalt principles. But even if you as a non-designer know the Gestalt principles, you won't know how to achieve good graphics.

Thus, there are checklists floating in the net for checking a website for good usability, but it is after the design, not while designing. It's not having it in mind while designing, like having design principles in mind while painting.

Or in plain words

I need to explain "how to achieve a good usability" for designers.

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  Do you know a good reference or article tackling this task?

  
  


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  What do designers need to know about usability?

  
  


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  How can one explain the concepts behind usability easily?

  
  

I hope this question is not offtopic. I'm not asking it at UX.SE, because for this guys everything will be so cristal clear. It is hard for an expert to explain things for non-experts easily and understandable. You are the target group, that's why I ask here.