Here are some adjustments you could make if the audience seemed to be losing interest:
- Ask questions.
- Have a member of the audience come to the front of the room and help you with a demonstration.
- Conduct an informal poll (“How many people think that…?”).
- Introduce a brief, interesting digression (go off topic for two or three minutes).
- Use a brief anecdote (preferably one that has something to do with your topic).
Each of the above adjustments has the advantage of offering a change of pace, and if your audience has given the appearance of losing interest these can turn that around by reminding the audience that there is a reason for them to listen.
Some audiences react to different things than others, and you will normally be able to tell what it is that your presentation lacks by reading the faces of your audience. If they look slightly pained and confused, it may be that you are speaking from a vocabulary with which they are unfamiliar. If they simply look bored, then it may be that you are not telling them anything new.
Involving the audience is something which, done carefully, can get a presentation right back on track when it has been threatening to lose their attention. From something as simple as not wanting to be called up to the front and exposed for their failure to pay attention, to something as enjoyable as the ability to participate in a genuinely interesting diversion, this will cause people to sit forward and become more interested in proceedings.
It may also be that you have been speaking excessively formally, and have appeared distanced and humorless. Obviously, a lot has gone into this presentation and you may well consider it to be “no laughing matter”, but a certain lightness of touch can make the presentation flow better and involve the audience more. It is wise to avoid disrespectful humor, but some light self-mocking can go a long way to getting the audience on your side.