At a conference, your audience will usually sit for most of the day. So, understandably, they may become sleepy and have trouble following your talk. Have you considered adding some short physical exercise to your presentation, to make them wake up?
Interacting with your audience can mean a lot of different things. You could ask them a question and to shout out the answer or to use hand signs. Or you can make them do short exercises, in groups or on their own. But all of those interactions are usually done sitting down. Consider an activity where they have to stand up and move.
