A promise

We need to engage all the audience in the beginning of the presentation and the best way is to promise them how the presentation can help them in many ways. While starting, the presenter should provide a mental picture of how the presentation is going to help them for example," By the end of this presentation you will have known how to increase profits effectively." A promise like this makes the audience take advantage of presentation and as a result a way of gaining and maintaining audience attention.

Source: http://9attentiongrabbers.blogspot.com/