. . .ever.  Great advice from Rowan Manahan at Presenting Is Simple (It's just not easy).

"Your audience is not asleep because of boring data or crappy PowerPoint - they are asleep because you decided that there was something more important than producing an interesting, relevant, engaging presentation for your audience. They are asleep because you decided that all the rehearsal you needed was to fiddle with your slides for a couple of hours and mull over a few half-formed ideas the night before your talk. If 90% of presentations are average-to-poor, it's because 90% of presenters don't treat their audiences with respect."

I know Manahan is writing about presenting, but the advice extends beyond presentations.  The first rule of meetings:  Don't waste their time (even if that means not having the meeting).  Sort of a Hippocratic Oath for business.  RFPs:  Don't waste your audience's time.  You get the point.  Treat them with respect.

Be sure to watch the stunning video.  It is not a waste of your time.