Mostly, audiences love to be involved in a presentation. It engages their brains in a different way than just listening to a speaker.
There are lots of ways of engaging the audience. You might ask them a question and then take their responses. Maybe you could write up their responses on a flip chart or a white board.
You could ask them to do something – such as look in their wallets and purses, or look at their watches or phones. I remember being in the audience when a famous inspirational speaker, Zig Ziglar, asked us to look at our watches and see if the dial had Roman or Arabic numerals. When we looked and then turned back to him he then asked us what the time was. Of course we hadn’t noticed the time! Which was his point, about how we miss things if we’re not focussed on them.
Or you could ask them to talk to the person next to them, or behind them. Maybe to introduce themselves and chat for a few moments, to make the point how easy it is to talk to a stranger.
Or you could ask for a volunteer to join you at the front so that you can question them.
Alternatively, you could ask them to handle or examine an object or a number of objects that you give them. And then answer a question about it.
Or you could ask them to write a list of things to do tomorrow, if you were giving a talk on time management, or maybe write down those things that are important in their lives or jobs.
Perhaps the best way to involve your audience is to construct your talk in a way that people can identify with your points and examples. For example, if you speak about your children it’s likely that the audience (if they’re adults) will think about their children or when they were children.
Asking them to make notes about what they could do from the ideas in your talk, or to talk to the person next to them, or simply to think about it, will engage them and will help you to become a more effective and memorable speaker.