When listening to music, think about the elements that you hear:
Rhythm - fast, slow, symmetrical, consistent
Texture - one "voice" only (monophony), one melodic "voice" with accompaniment (homophony & melody-driven homophony), many "voices" in the same rhythm or "hymn-like" (homorhythmic), more than one "voice" sounding in different melodies and rhythms (polyphony)
Timbre (Color) - nasal, hollow, deep, etc. (different instruments have different timbres, hence why they can play the same note yet sound different)
Line - is the musical line jagged (predominantly made of skip-wise motion), connected (predominantly made of step-wise motion), or both
(The first two are available at Bryn Mawr, the latter three are available at Haverford)
Each instrument has it's own timbre and "feel"--try listening to a few to see what you think.
The Classical Music Navigator is a database which allows you to browse by "points of interest"--in other words, if you find a composer you like, it will help you find others with simliar sensibilities.