Writing a Cover Letter for the Music Industry is no different than for any other industry. Your goal is to make a professional first impression and get an interview or audition. Even if the job posting doesn’t specifically ask for a Cover Letter, you should provide one as it is always expected and gives you the chance to show your professionalism.
Pay close attention to the terms used in the job posting, and make sure to address each point included. Keep in mind that some companies use software algorithms to screen out applicants, so your letter might never get read by a human. This also means you should avoid using a picture or any graphics that would not be readable by the applicant processing software.
A few more tips: read the job posting very carefully; make sure to include your contact info, mention the job you are applying to, send the letter to a person, be enthusiastic in saying why you want the job and are a great fit, and end with a “call to action” such as asking for an interview or audition.