The focus of the rubric is based on the subject that is to be assessed and the breadth of the subject matter the rubric is to assess.  Care should be taken to select a focus that is clear to others as well as to yourself exactly what the rubric will measure.  A rubric can be either holistic, globally measuring a single trait, or analytic, breaking down a complex concept into constituent parts.

Consider a rubric that is supposed to identify how well any of the students in band played an assigned section of a piece the band was working on.  This rubric would be holistic and it would be generic.  That is, there is to be one scale that measures the totality of each student's playing no matter if the student plays flute, clarinet, saxophone, oboe, trumpet, trombone, or percussion.

A good method for assuring that the rubric being developed stays "on-track" or remains focused on its original intent is to clearly write the focus at the top of the page on which the rubric is being developed.  For the generic rubric described in the preceding paragraph, the following might be appropriate.

This generic rubric will determine the overall performance level of band students in playing a section of practiced band music.

Any musical performance can be broken down into many different aspects that have the potential to be assessed.  For instance, the intonation, technical facility, rhythm, and musicality are other parts of a musical performance that could be assessed.  One approach would be to develop a multiple analytic rubrics to provide students with information about how well they are performing on each of these musically meaningful dimensions.  Such a set of multiple rubrics might have the following description.

This generic rubric will determine the overall performance level of band students in playing a section of practiced band music.