Listen to the piece of music multiple times. Note specifics about the piece such as the type of piece, specific instruments and its harmony. Consider specific transitions within the piece and any unique style considerations that you notice such as its dissonance and the inclusion of more modern instruments.
Identify the period in which the piece was composed. Modern classical music is identified by a wilder tone and a predominance of cymbals and triangles. Modern classical music also uses more dissonance than earlier periods of music. Classical music within the Romantic period is marked by powerful dissonance. The increased use of the piano is another mark of the Romantic period. The Classical period is noted by simpler music than the complex pieces of the Baroque era but includes more changes in the mood and tempo than earlier music. The Baroque period contains the most complex instrumental performances. Baroque music avoids wild changes in the mood or tone and tends towards a rising complexity and complex form.
Reference the specific instruments you heard within the piece. The presence of electric instruments or synthesizers marks the piece as Modern. Piano sounds are indicative of the Romantic period. Swift changes in the primary instrument and a reliance on stringed instruments marks the piece as being from the Classical period. The Baroque era was known for the use of the baroque guitar, bass viol and the harpsichord.
Identify the type of piece to which you are listening. Concertos are identified by the competition or cooperation of two different episodes of music. Symphonies use a central tonal harmony to guide other instruments and push the piece forward. Minuets are slow, celebratory pieces known more for being graceful than complex. Sonatas utilize either a single instrument or isolated harmony.
Consider the major composers of the period in which the piece was composed. Reference the type of piece and major instruments. Each classical piece of music was constructed with these specific elements and each gives you an idea of the era it was composed within, and therefore which composer may be responsible for the piece.
Listen to classical music regularly with these elements in mind. Experience with classical music helps attune your ear to these elements and provides a foundation for identifying pieces in the future.