If you've read many of my blog posts or listened to any of my podcasts, you'll know that I mention this one a lot. This is the absolute BIGGEST mistake that almost everyone who presents (even me on occasion) will commit. We start our preparation by creating the slideshow (or other visual aids). This part of the preparation typically takes longer to complete. As a result, we will start doing this part way too early in the process. You will save yourself a lot of time and a lot of stress if you figure out what you want to say first. Then, after you have a pretty good presentation, design visual aids to help you explain the content.
A few years ago, I was called in to help a team of engineers practice a group presentation to one of their big clients. The vice president of the engineering firm along with the head of the marketing department made a PowerPoint deck for the entire group. So, they created the slide-deck by receiving input from the other four presenters ahead of time. However, the other four presenters were not intricately involved in the process. So, I arrived in the meeting room, and the presenters were confused and irritated already. Each of them were trying to say interesting things based on the visual aids that had been pre-created for them. So, they were adapting what they wanted to say to what was on the screen. To be blunt, it was really, really boring. The four speakers who had little control over the slideshow were extremely nervous.
Luckily, I had seen this type of challenge before. So, I had each of the presenters disregard the slideshow temporarily and re-design their actual speaking part. We spent an hour or so re-creating the speech. Then, I had each of them practice their part of the presentation a couple of times. All total, this took about half a day. They all began to feel more comfortable with their speech. Finally, we redesigned the visual aids to help each of the presenters better explain his or her content. Interestingly, a couple of the presenters didn't use a slideshow at all. They chose to use props and posters instead. (These visuals were better for their part of the talk.)
Design your presentation first. Then, figure out what visuals will help you explain the content better.