How I learned how to do Sfx, foley, and scoring is to use scenes from films I have not seen before, so I have no pre conceived notion of how things sound like, especially with scoring. Then I choose a scene, convert to QuickTime and mute the audio tracks. Then I design away and mix. Then I compare the way i edit with the actual sound from the movie. Very good leaning tool. I would do a Hollywood action, romantic comedy, documentary and a thriller, and maybe an old classic film that never had a score and see how adding music, sfx, foley adds or detracts from it.
Alternatively you could find an indie film director and score a short on spec.