Below is an interesting article from the FilmScoreMonthly site. It discusses a little bit of the process.
http://www.filmscoremonthly.com/features/skelton.asp
Also, especially if you want to score films yourself someday, check out some commentaries which appear on DVD’s. Danny Elfman has done a few, Pee-Wee’s Big Adventure, PotA, Edward Scissorhands… Elliot Goldenthal has a few commentaries: Titus, and Final Fantasy… also i thought Don Davis’s commentary on the Matrix DVD to be very insightful.