Build a (user) story. Why are presenting? What do you want to accomplish by taking to these people? Based on what they already know, how much background do they need? Your don't build features by adding buttons and sliders - you figure out user stories by asking why a dozen times. It's not quite the same dynamic but you can roughly go through the same exercise, even if it's just in your head.
The other big thing is to reduce text content to the bare minimum. Remove sentences (move them to speaker notes, if you want). Keep rephrasing things to make it shorter. If you have lots of text on screen people read it and don't pay attention to you. If you're reading the text verbatim, you might as well just email your content and not waste the time talking.
Visuals are good when possible. Even dumb stock photos can work: for example, if you're making an argument that your onboarding process is too complex, a photo of a crazy highway interchange can help reinforce that. It certainly leaves a more lasting impression that a 9-point bulleted wall of text.