When people get on their feet to make a presentation, they normally go into a default, presentation-mode of speaking. It's as if they take off their personality and leave it on their chair, thinking, 'I'm about to present; I won't be needing this for a while.'
Which is why most come across as stiff, robotic, formal, wooden and expressionless. And worst of all . . . dispassionate, as if they don't care about their topic. They talk at the audience rather than to them, delivering a set of facts, bullet points or data with all the passion of someone reading a grocery list. But if you think of the people you'd regard as really great speakers (whether they're politicians or colleagues) they're probably people who injected passion and their personality into their vocal delivery.
If you want to keep your audience's attention, you have to have a conversation with them rather than just deliver facts. Now I don't mean have a dialogue with them. There are times when this might be appropriate, but you run a serious risk of losing control if you try it, and most of the time you won't have enough allocated time to risk it. A dialogue is between equals, where each party has just as much 'right' as the other to have their say. This is a presentation. You probably want people to speak up if they haven't understood something, but 90% of the time, the communication is going to be one-way.
What I mean, is talk in a conversational manner. Conversation is the first type of verbal communication we learn, and we then spend most of our lives practicing, perfecting and refining it. In other words, it's what we're used to.
It's only very occasionally that we have to communicate in any other way. So much so that when we find ourselves having to listen to a monologue, speech or presentation for any length of time, it's actually quite difficult. So we have to create the perception for the audience that they're taking part in a conversation, even though they're not.
If you're reading this in an office, have a look around and see if you can find two people having a conversation right now. If you can do it without them noticing, watch and listen to them. They'll look each other in the eye. They'll be animated, using facial expressions and other body language to help make their points. Their voices will contain intonation and they'll emphasis certain words or phrases to make their points. Their voices will also speed up and slow down, rise and fall in volume.
Now how much people do any of these things obviously depends on their personality. Some people are naturally very expressive, some are naturally impassive. Some naturally speak loudly or quickly, others softly and slowly. We're all different. But we do all do these things. Why? Because all of these things play a crucial role in holding the other person's attention during the conversation.
That's how we converse. Again . . . it's what we're used to. So you have to get out of 'lecture mode'; stop talking at and start talking with the audience.
BUT . . . and it's a BIG 'but' . . . having said all that, you must remember you're NOT having a conversation. You're presenting. So don't converse, but present in a conversational manner. There's a big difference.
When people who are naturally quiet or laid-back try to converse with an audience, they usually come across in a very low-key, quiet manner. When you're a few feet away from the person they're talking to (as in a normal conversation) it's fine. But in many presentations you're ten, twenty, even fifty feet or more away from some of the audience. And then it just doesn't work.
The bigger the distance between you and the audience, the more emphasis you need to give. In intonation, emphasis, volume and hand gestures. That's why actors are very different performing on a theater stage than on TV. The distance is obviously much greater in the former, so everything they do has to be exaggerated.
That's also why a politician speaking at a rally might sound perfectly appropriate to her immediate audience, but completely manic and 'OTT' to people watching clips of her speech at home on TV. Think of the difference between President Obama's vocal delivery when on the campaign trail, firing up a live audience of thousands, and on TV delivering a 'fireside chat.' It's completely different.
So with a large audience (or when even a small-ish audience is some distance from you) you need to exaggerate. This will seem strange, uncomfortable, even false. But it's not false. It's not acting, which is pretending to be something you're not. It's being yourself, just . . . a slightly exaggerated version of yourself. And while it may seem a little larger-then-life in your head, to those sitting some distance away it won't be. The extra distance will 'flatten out' your slightly exaggerated delivery so that by the time it reaches them it'll sound completely natural.
This is why many people feel very uncomfortable speaking to an audience they know well, such as close colleagues. They feel very conscious that they're speaking in a way that's not 'normal' and their friends, colleagues and relations will spot the difference and think, 'What's he talking like that for?' In reality, if you get it right, they won't even notice.