sorry, when you said "I'm not looking for program specifics but the General rules" I thought you wanted info on the why of modelling,  misunderstanding there........
Rules?
Lighting has to be natural, shadows are a good thing...... the pose has to be comfortable, like a real person was in the scene.  forget what I said earlier, just make it pretty to start with.  practice practice practice.  try to emulate photographs. 
just play with the programs for a while, use all the special effects, get them out of your system (your system, not the computer's) and then just do your thing.
Check out Dr.Geep of Poser U for more down to earth info.