Again, take this with a grain of salt, because I'm not very good at lighting:
A big, crucial key in getting started with learning lighting:
Poser's default lights make no sense whatsoever.  By default, you have three Infinite lights - an Infinite light is basically like the Sun.  The light from Infinite lights does not spread, as it would from a light bulb in a lamp or light from a candle, it's "coherent".  While shadows will blur based on the shadow settings for a particular light, how much the light will spread and at what angle depends on the light type.

Three Infinite lights (Poser default) basically means you have three Suns.  While you can get away with this in very simple scenes with no backdrop and a pretty close-in composition like a head portrait, if your scene is complex at all, then many viewers will have problems with how the light looks - because it's very unnatural, we don't have three Suns.  For outdoor scenes, you probably want only one Infinite light, to simulate the sun.  For indoor scenes, you probably don't want any Infinite lights at all, except for pretty low-intensity "fill" lighting (e.g. trying to fake radiosity).

What I do for indoor scenes, and what a lot of people do, is some combination of one or more spotlights - usually one overhead at some angle, and often one oblique, lower spotlight to bring out some contrast on the model's features, and some kind of "fill" light (often Infinite at pretty low power) to keep shadowed spots from being completely black.  Many times my fill light is coming from a very low angle and somewhat behind the model, to simulate light bouncing off of the floor or from a backdrop.  Typically I'll turn off shadows for the fill light.  This is one example:
http://www.renderosity.com/mod/gallery/index.php?image_id=1364153&member

Main light is a high power spot, nearly straight overhead, which casts the floor shadow; a second light is off to the viewer's right, and casts the shadow on the wall; and one fill light, very low power (perhaps a bit too low) almost parallel to the floor and straight on at the models.

Another example:
http://www.renderosity.com/mod/gallery/index.php?image_id=1392994&member
The same basic approach here, although there is no backdrop; and an example of how organic it can be sometimes, that character's hair tends to put a heavy shadow on her face, so I had to add an extra middle power spot with a tight angle just big enough to light her face up a bit.  The extra spot is in a completely unintuitive position, and it's just a one-time workaround for the problem with that character and hair, it wouldn't be appropriate to do for every character.

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