This is a good question, something I've answered a lot in workshops but never blogged about. So here's what I think is really important about prepping short talks with PowerPoint presentations:
- Create the number of slides you think you need, then get rid of a couple! The time just rushes past in short presentations, so when it comes to your PPT (or whatever else you're using) you almost always need less than you think. Five slides for a 15 minute presentation may often be enough.
- Simplicity is never more important. Simple slides are better anwyay (image-rich, a little text as possible, no bullets) but are especially vital when you only have a very short window in which to convey your information. The messages need to stick, so make them easy to understand and support them with relevant images.
- Signpost to more detailed information. Have a blog-post already published which goes into more detail than your 15 minutes will allow, and use a customised bit.ly URL to share the post in an easy-to-remember link at the end of your talk.
- Structure is still important. Audiences find structured presentations easier to remember and understand, even for very short talks. So try to have a beginning, a middle, and an end clearly signalled (both in what you're saying and in your slides)
- Consider doing a 20:20. A 20:20 (also known as Pecha Kucha) technique involves having 20 slides, each of which automatically moves on after 20 seconds. These are acually really fun to do (the trick is to keep talking rather than stopping to wait for the slides to catch up) and force a real discipline in terms of the economy of your delivery. A 20:20 takes just under 7 minutes and it's amazing how much you can cover in that time if you practice. (I know point 5 directly contradicts point 1, but the approach is SO different with Pecha Kucha it's a whole different ball-game...)