If you are giving a presentation you may think the most interested people are in the front and the least interested in the back. There is some truth to this, but studies have shown in academic situations there is more of a "T" to how people sit.
This means that the most engaged audience members usually sit in the front and in the middle, all the way to the back of the room. So keep an eye out for people dozing off in the other sections, but folks sitting up front and in the middle "T" are usually into you.
Where do you sit for presentations? Where do you focus when you speak to a group?