Books are nice, don't get me wrong, but you also need to do a LOT of listening as well.
I would highly recommend that you get a copy of "Stars Wars" Special Edition Soundtrack, the one from 1997 if at ALL possible, by any means. If you can't find it, I guess the Sony Records version will have to suffice but the '97 issue is by far, the most superior version of this music to date.
If you listen to this, ad naseum,you will, unconsciously, assimilate the rudiments of style and technique for everything involved in what you are striving to achieve. No, the goal is NOT to turn yourself into John Williams but, to get a first-class education from, arguably, one of the best composers EVER to grace a Hollywood Soundstage.Sharpen up your ears and also, read everything you can about the soundtrack-it can only benefit you in the long run.
For the technical side of things, I offer up this invaluable document:
http://www.malonedigital.com/starwars.pdf
Burn a copy of this for yourself,put it in page protectors and a notebook. It is reference material that will never be old, in musical/technical terms.