Too many scientists prepare a presentation by digging into a folder with hundreds of PowerPoint slides and asking the question, "What can I cut?" The problem is that everything seems essential and the presentation ends up containing far more information than the audience can digest. Coherence is lost and the talk is little more than a "data dump."
"Build up" don't "cut down." Identify a concise narrative (symbolically illustrated above by a single slide) and then add detail given the available time and ability of the audience to understand. The September 21, 2015 "tip" gives three alternative ways to develop that narrative. Once the narrative is in place, try giving a two minute version of the talk without slides. Then try a five minute version with slides, then a ten minute version, etc.
Not only does the "build up" strategy allow the speaker to maintain coherence, it helps cope with other problems. Your talk may be scheduled for 45 minutes, but the "build up" strategy will prepare you for a 30 minute version should your time be shortened (no, the answer is not to talk faster when your time is cut). Also having developed a simple narrative at the beginning, you will have a story and structure that is accessible to a wide audience, even if some of the details are only comprehensible to a few specialists.
