The best briefing

The worst presentation briefing (and as a result most time-consuming presentation design project) is a long deck of slides full of bullet points that have been shortened (hey, we learned about being concise) to such an extend that they have turned into meaningless, generic prose.

The best presentation briefing (and start of a rapid presentation design project): the audio track of a 15 minute video of the actual presentation, the existing slides are not really needed.