Think about the last time you gave a presentation. Were you nervous? Excited? Scared to look stupid in front of your boss? Confident in your ability to wow the others in the room? These emotions reveal that at our core, our biggest desire when presenting is to make ourselves look good. This desire is antithetical to a good presentation and harmful if not addressed directly.
Our first priority must be the audience. They're giving us their attention, and we have the responsibility to use that precious resource wisely. If we waste it, they'll be less likely to give us this attention in the future. While we may think we're being clever with our sales pitch, people are smart enough to see right through us (even if what we're selling is our own self image).
Prioritizing the audience requires us to adapt our message to them. This doesn't mean dumbing it down. As an example, consider presenting some interesting result to two audiences: a coworker and the CEO. The CEO of your company will require more context than your coworker. This does not mean that the CEO is somehow dumb; it means that she isn't as familiar with your work (for obvious reasons).
Instead of prioritizing the audience, we often prioritize ourselves (typically without even realizing it). We want to appear smart, competent, and confident in front of others. Subconsciously, this leads us to present in ways that obfuscate the truth in order to make ourselves appear intelligent. If our audience leaves a presentation thinking that we are a genius, we have probably failed to explain our idea in a way that they can understand.
We should go into presentations hoping our audience finds what we say to be "common sense". If they agree with what we've said without much questioning, we have likely guided them through our ideas in a way that is easy to understand.
If you've never given thought to the specific people that are in your room, try it out. Do research to understand what they know and how they best digest information. If you already do this, consider doubling the amount of time you spend here.
When we go into presentations seeking to look like a genius, we end up confusing rather than enlightening. Those who try to look impressive ultimately fail to do so, but (paradoxically) those who give up on impressing do.