Once I filled out an application I got a call. I came in and the interview process was basically just a conversation with the manager and got an offer afterwards.

Most of the questions were centered around schedule availability and effectiveness to work with others in a team. If you has been engaged with the company before (whether as someone who has taken lessons there or as a frequent customer) it is definitely a plus. Proficiency with musical instruments does not help you as much as it would for a full-time employees so do not invest a lot of your time explaining how you are skilled in playing i.e. the violin, guitar, flute, etc.