Make sure that you arrive early enough to play with the camera before the talk starts.
Even if we designate the "speaker camera" and the "audience camera", it doesn't mean that they need to be always pointed to the speaker or audience. During the talk, for example, the audience camera can be used as a second shot of the speaker. And the speaker camera can also be used pointed to the audience, mainly if there is a discussion with many people distributed around the room.
Try to avoid moving while your camera is selected (tally light is on). If you have to move the camera, move it slowly and smoothly. Some tripods are not very good, you may need to move the camera with one hand hold the tripod with the other to assure that.
Try to avoid showing people that are obviously asleep in the audience, instead, do panning shots of people who are paying attention.
When the speaker is pointing something at the screen, it's usually a good idea to show where their hand is pointing, otherwise, those watching at home have no idea in which direction they should look.
Communicate with the director as you can, he has the whole picture of the room. Look at him once in a while so he can ask you to do a specific shot or panning.