1. Using slides as a substitute for preparation.
"Working on the deck" until the very last minute is tempting. We try to make sure it LOOKS perfect before taking it out in front of people. However, by focusing too much on the slides beforehand, you may run out of time to practice your actual delivery. Your audience prefers well-told, relatable stories structured along familiar patterns. If you haven't prepared, you've already lost. So instead of pushing pixels around until the deadline, take PLENTY of time to work on your delivery. (Try one hour for every five minutes worth of content).
2. Using slides as a substitute for yourself.
Unless you're this guy, you're not likely to connect emotionally enough to move an audience with the content on your slides alone. Why? Because humans prefer to hear information from other well-spoken humans. Also, if you're going to let your slides carry the responsibility of communicating, you might as well not be there. Research has proven parallel processing (asking audiences to process two or more streams of information simultaneously) effectively cancels out each message. You're the star of your talk. Your slides can be your sidekick.
3. Using slides for too much information.
1. A lack of strategic discernment when collecting and preparing content.
2. An expectation the deck will be read after the presentation.
A deck is a medium.
A presentation is an event.
A deck is a tool that can be used to complement a speaker.
A presentation is an opportunity to build, change and reinforce beliefs in a one-to-many setting.