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Even before you start off with a CBT plan - the most important thing is to know the content, that is to know what is needed to be known first. Content is definitely the King. Secondly, you will need to be organizing the content into managable bits of information that a learner can digest.
Thirdly, you would need to be understanding the relationship between these two pieces(bits of information + learner) and the CBT software you are going to use to deliver and test the content. Fourthly you would need to look at utilizing one of a variety of methods within the CBT framework (e.g. some video, some text, some sound). Nowadays, everyone thinks in terms of Universal Design for Learning (UDL). A bit of creativity is also a wonderful thing to bring to the equation.