In classical music the composer is the main force in the music's texture and interpretation. Very specific instructions for the feeling of a piece and dynamic markings are included by the composer to guide the performer's interpretation of the music. Percussion is used mainly as a coloring for the music and as a support for other sections of the orchestra. In popular music, it is the drummer's job to help create and maintain the feeling or essence of the music being played.
All music is written with definite patterns or sequences of melody, harmony and rhythm.
If the music has a beginning and an ending it has form. The 12-bar blues, or some derivative of it, is used in all styles of popular music from country to rock to jazz. It is a 12-bar chord progression based on the first, fourth and fifth notes of a diatonic scale. The 32-bar song form is very widely used in contemporary music from pop to jazz to Broadway shows and movies. Knowing the form of a piece of music is immensely helpful in making logical sense of the music and following an arrangement.