Yeah, yeah, we know that our audience matters and we should take it into account, but in practice, most of us dive straight into designing the slides.
Thinking of your audience is especially important for sales presentations. I have had a few clients situations where I was asked to help design decks that are used by a sales force that targets small business owners.
In those cases I actually imagine the actual/real owner of a restaurant or pharmacy who I have seen recently and wonder what it would take to convince her.