All of the comments are good but somewhat miss the point. I have done television shows with and without studio audiences.

If you have a studio audience there is no good reason not to play to them as you would in a normal performance and pretend that the camera does not exist.

If there is no studio audience then your audience is the the viewer at home. The only way you have to connect with that person is to appear to make eye contact. this is only achievable by looking directly into the camera, there is a little red light on the darned thing look at that light. To the viewer it creates the illusion of having you look directly at him or her.

That has been my experience, at any rate. Take it for whatever you may think it to be worth. Break a leg.

Stephen