Here's a lively paper on the ins and outs of giving a presentation and communicating ideas.
"In the newspaper business they teach you to put the least important stuff at the end, so if your story was cut for length the reader wouldn't miss much. But in a presentation, it helps to start with the end, because that's when the results should start coming in.
There are two ways to start from the end.
The first is asking yourself what results you want from the presentation. Is it sales? Understanding? Recruits? Strokes? Whatever you're looking for, that's where you need to start, because without a clear outcome in mind, there's no way your presentation will come out clear.
The second is to state your conclusion. Larry Gottlieb calls this the 'conclusion first' approach. First impressions last longest. If you don't say the one thing you need to say right up front, it may never get heard.
Starting with your conclusion also tells the audience you won't waste their time with preliminaries."