There are all sorts of miracles that soft window light, ample fill, appropriately diffused lenses, and a strategically moving photographer can achieve!
As you will see clearly from what I am about to say, I'm not a portraiteer- haven't even tried. I am thinking mostly about landscapes these days. Nevertheless I would go about this the exact same way that I'd approach any landscape: foremost enumerate the best things about the scene and think about how to make them come to the fore. Unusual or unexpcted elements can become extraordinarily powerful in any composition. Now, with portraits you have all kinds of technical and creative power that you don't have with landscape: you can totally control the lighting, you can credibly diffuse or work with very limited depth of field without it being seen right off as an "effect", you can make big adjustments in the orientation of yourself and your subject... very quickly. Just think about all that power you have and how you're going to use it for good!
[Okay I just realized why I am afraid to try portraiture: too many degrees of freedom.]
Books? There must be millions on portrait lighting alone. I think the thing to do is go to the bookstore and find some examples that you like, and learn how to start taking them apart in terms of what lighting techniques were applied. Right on this site, in the gallery section, I think you will find some masterful examples and people willing to discuss how they worked the shot.