Some ideas:
1. Kinds of instruments (Harpsichord?- Baroque. Trombones?-
Baroque or Romantic. Harps?- Classical, mostly Romantic.
Saxophones?- Late Romantic and 20th Century. etc.)
2. Emotions/Tones you would find ( Soft, Serious- Baroque or
Classical. Anger, Depression- Romantic or 20th century. Chaos- 20th
Century, some Romantic)
3. Styles (too many to go through ex. 20th century - atonal,
unusual, harsh chords)
4. Nowadays, all these can be copied (ex. soundtracks) in any
way.