I sometimes help with hiring; although, not in music.
The biggest thing by far is experience. The more experience the better. Now, of course, being in college the experience will be limited. But any volunteering, helping with clubs, being busy during the summer the better. When I was in college, my work study all related to teaching. I then volunteered and helped in the community. My resume was much longer than my peers and it gave me an advantage
Next is certification. When a principal is filling a position, they are looking for how to fill different spots, and sometimes this may be half a teaching unit. Now, it does not apply as much to music, but still having a certification from K-12 instead of just elementary or just secondary helps, having additional certifications helps.
Finally, the interview. I've seen great candidates on paper come in and do terrible in interviews. Be likeable, and be confident. Stay away from both extremes. No one wants a fire hose of information, but also, it's okay to think over an answer. In fact, some of the best interviews I've seen, the individuals will take ten seconds to think about the answer, write a few notes down and then attempt it. Also, the principal and committee is asking itself is this someone whose personality will mesh well with the rest of the faculty.
Now I can think of a few other things, but in general when you say music are you referring to choir, band, music theory, in general?
As to grades, as long as it's above a 3.0, I wouldn't worry about it. I would, however, use the university's career services department.