I didn't have time to read all previous replies, so I hope I won't repeat too much
Anyway when I want to analyze a score the first thing I do is look for contexts,
what theme is associated with which character/place/event/notion etc...
And then look for recurrences and variations,
for instance in the "Lord of the Rings" score by Howard Shore (just an example),
the motiff for the "Ring seduction" (basically a low-end rhythmic pattern) can be heard often throughout the score, elegantly entwined with the Shire theme (when Bilbo, Frodo or Sam are being seduced), with the Fellowship and Gondor themes (when Boromir is seduced) etc...
Try to figure out "why" (not "how") the composer wrote things as he/she did.
Listen for anything distinct, be it instrumentation, rhythm, sound, etc,
sometimes even a thing as overlooked as panning can have a meaning in a certain context.
And the best advice I can give you is don't bother with bad scores.
Only study good scores from good composers and orchestrators.
A few simple and yet good scores to start with would be Cinema Paradiso (E. Moriconne), Conan the Barbarian (B. Poldouries), Robin Hood: Prince of Thieves (M. Kamen), or Harry Potter I (J. Williams).
Good luck,
Omri.