NB: These guidelines are written from the perspective of those in Chicago, the mid-latitudes of the northern hemisphere.  Those in the southern hemisphere should substitute south for north in these recommendations.  Those in tropical latitudes will see significantly less difference between north and south light than those in temperate regions.

When looking for the optimal lighting, a room with good natural light, especially from north-facing windows, is a suitable place to start.  North light is diffuse by nature and will cast softer shadows, and its intensity is apt to vary less over the course of the day.  Eastern, western and southern exposures are also good, but the intensity of the light will vary more over the course of the day.  For example, an east-facing room that is perfect in the morning, may need much more artificial light in the afternoon. 

If the natural light is insufficient in the room you choose, it can be supplemented by artificial lighting to reduce shadowy areas.  Soft, indirect lighting is best.  Strong, direct light will produce harsh shadows.  Avoid strong light sources coming from below because they can give the speaker a sinister appearance.  Avoid strong light from behind unless you want to appear in silhouette like someone in a witness protection program.  An adjustable lamp can be aimed at a wall or ceiling, especially one painted white or another light color, to produce a more diffuse light.