- Get out into the audience: Walking into the audience accomplishes all sorts of things that can help speakers before they lose the audience. It puts you on their level, makes you more accessible and humanizes you. Better yet, it almost instantly forces people to follow you--especially if you walk around. Audiences tune out when they think they know what to expect; if you move out from behind the lectern and come down the aisle, there's no telling what will happen.
- Gesture: Judiciously used, a gesture that underscores a point can have the same effect in a smaller way. Look for the points of emphasis in your speech and determine whether a well-timed gesture can bring the audience back.
- Get the audience involved: Instead of lecturing at them, take an instant poll--don't tell them your point, ask them what they think and take the measure of the room. Audiences, more and more, want participation, not passive listening. Engage them by asking questions and commenting on the results, or ask them what their experience has been. You'll learn something about them and you'll get their attention.
Those all are better than overemphasizing your point, increasing your volume or showing your panic--unfortunate reactions I've seen from speakers who fear their audience is slipping away. The best technique? Plan a speech designed to do all these things from the start, and avoid the problem entirely.