You need to understand the basic musical notations and symbols first. Then, pay attention to the story and how it relates to the music elements presented.
To read music comics well, start by familiarizing yourself with common musical terms and their visual representations. Also, look for cues in the art that enhance the musical experience. For example, the expressions of the characters or the way the panels are laid out can add to your understanding.
The key to reading music comics is having some background knowledge of music. Know about different instruments, beats, and musical styles. And don't forget to follow the flow of the story as it weaves in and out of the musical aspects.